diff --git a/.gitignore b/.gitignore
index 02634697bf..8808186ee8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,6 +4,7 @@ docs/_dist
 mocha.js
 .karma/
 !lib/mocha.js
+/types
 
 #########################################
 # NON-MOCHA STUFF GOES BELOW THIS THING #
diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000000..556377e4f3
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1 @@
+export = import('./types/mocha');
diff --git a/lib/cli/options.js b/lib/cli/options.js
index c87552c542..3227033dfd 100644
--- a/lib/cli/options.js
+++ b/lib/cli/options.js
@@ -165,9 +165,8 @@ const parseMochaOpts = content =>
 
 /**
  * Given filepath in `args.opts`, attempt to load and parse a `mocha.opts` file.
- * @param {Object} [args] - Arguments object
- * @param {string|boolean} [args.opts] - Filepath to mocha.opts; defaults to whatever's in `mocharc.opts`, or `false` to skip
- * @returns {external:yargsParser.Arguments|void} If read, object containing parsed arguments
+ * @param {import('./options_t').MochaArgs} [args] - Arguments object
+ * @returns {import('yargs-parser').Arguments | void} If read, object containing parsed arguments
  * @memberof module:lib/cli/options
  * @see {@link /#mochaopts|mocha.opts}
  * @public
@@ -210,11 +209,10 @@ module.exports.loadMochaOpts = loadMochaOpts;
 
 /**
  * Given path to config file in `args.config`, attempt to load & parse config file.
- * @param {Object} [args] - Arguments object
- * @param {string|boolean} [args.config] - Path to config file or `false` to skip
+ * @param {import('./options_t').MochaArgs} [args] - Arguments object
  * @public
  * @memberof module:lib/cli/options
- * @returns {external:yargsParser.Arguments|void} Parsed config, or nothing if `args.config` is `false`
+ * @returns {import('yargs-parser').Arguments | void} Parsed config, or nothing if `args.config` is `false`
  */
 const loadRc = (args = {}) => {
   if (args.config !== false) {
@@ -227,11 +225,10 @@ module.exports.loadRc = loadRc;
 
 /**
  * Given path to `package.json` in `args.package`, attempt to load config from `mocha` prop.
- * @param {Object} [args] - Arguments object
- * @param {string|boolean} [args.config] - Path to `package.json` or `false` to skip
+ * @param {import('./options_t').MochaArgs} [args] - Arguments object
  * @public
  * @memberof module:lib/cli/options
- * @returns {external:yargsParser.Arguments|void} Parsed config, or nothing if `args.package` is `false`
+ * @returns {import('yargs-parser').Arguments | void} Parsed config, or nothing if `args.package` is `false`
  */
 const loadPkgRc = (args = {}) => {
   let result;
@@ -275,7 +272,7 @@ module.exports.loadPkgRc = loadPkgRc;
  * @param {string|string[]} [argv] - Arguments to parse
  * @public
  * @memberof module:lib/cli/options
- * @returns {external:yargsParser.Arguments} Parsed args from everything
+ * @returns {import('yargs-parser').Arguments} Parsed args from everything
  */
 const loadOptions = (argv = []) => {
   let args = parse(argv);
diff --git a/lib/cli/options_t.ts b/lib/cli/options_t.ts
new file mode 100644
index 0000000000..bbcb20f519
--- /dev/null
+++ b/lib/cli/options_t.ts
@@ -0,0 +1,7 @@
+export interface MochaArgs {
+  /** Path to `package.json` or `false` to skip */
+  config?: string | false;
+  package?: boolean;
+  /** Filepath to mocha.opts; defaults to whatever's in `mocharc.opts`, or `false` to skip */
+  opts?: string | false;
+}
diff --git a/lib/cli/run-option-metadata.js b/lib/cli/run-option-metadata.js
index d0bc92ffbe..cb0ef0e87d 100644
--- a/lib/cli/run-option-metadata.js
+++ b/lib/cli/run-option-metadata.js
@@ -9,7 +9,7 @@
 
 /**
  * Dictionary of yargs option types to list of options having said type
- * @type {{string:string[]}}
+ * @type {Record<string, string[]>}
  * @private
  */
 exports.types = {
@@ -63,7 +63,7 @@ exports.types = {
 /**
  * Option aliases keyed by canonical option name.
  * Arrays used to reduce
- * @type {{string:string[]}}
+ * @type {Record<string, string[]>}
  * @private
  */
 exports.aliases = {
diff --git a/lib/utils.js b/lib/utils.js
index 805d98d463..91856463b9 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -708,7 +708,7 @@ exports.isPromise = function isPromise(value) {
  * Clamps a numeric value to an inclusive range.
  *
  * @param {number} value - Value to be clamped.
- * @param {numer[]} range - Two element array specifying [min, max] range.
+ * @param {number[]} range - Two element array specifying [min, max] range.
  * @returns {number} clamped value
  */
 exports.clamp = function clamp(value, range) {
diff --git a/package-lock.json b/package-lock.json
index e66be18a00..f276bc18bf 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -416,9 +416,9 @@
       }
     },
     "@types/node": {
-      "version": "10.12.29",
-      "resolved": "https://registry.npmjs.org/@types/node/-/node-10.12.29.tgz",
-      "integrity": "sha512-J/tnbnj8HcsBgCe2apZbdUpQ7hs4d7oZNTYA5bekWdP0sr2NGsOpI/HRdDroEi209tEvTcTtxhD0FfED3DhEcw==",
+      "version": "13.1.7",
+      "resolved": "https://registry.npmjs.org/@types/node/-/node-13.1.7.tgz",
+      "integrity": "sha512-HU0q9GXazqiKwviVxg9SI/+t/nAsGkvLDkIdxz+ObejG2nX6Si00TeLqHMoS+a/1tjH7a8YpKVQwtgHuMQsldg==",
       "dev": true
     },
     "@types/normalize-package-data": {
@@ -460,6 +460,21 @@
         "@types/unist": "*"
       }
     },
+    "@types/yargs": {
+      "version": "15.0.0",
+      "resolved": "https://registry.npmjs.org/@types/yargs/-/yargs-15.0.0.tgz",
+      "integrity": "sha512-TITCsNxRSDVmq3kPGuUdKZTPTfHeswsUGIjxSe8SB4EBKTPA0DO0y4yWI95kZ2hfqJAYxmu+gxzjOwdumB5S0g==",
+      "dev": true,
+      "requires": {
+        "@types/yargs-parser": "*"
+      }
+    },
+    "@types/yargs-parser": {
+      "version": "15.0.0",
+      "resolved": "https://registry.npmjs.org/@types/yargs-parser/-/yargs-parser-15.0.0.tgz",
+      "integrity": "sha512-FA/BWv8t8ZWJ+gEOnLLd8ygxH/2UFbAvgEonyfN6yWGLKc7zVjbpl2Y4CTjid9h2RfgPP6SEt6uHwEOply00yw==",
+      "dev": true
+    },
     "JSONStream": {
       "version": "1.3.5",
       "resolved": "https://registry.npmjs.org/JSONStream/-/JSONStream-1.3.5.tgz",
@@ -690,6 +705,12 @@
       "integrity": "sha512-/FQM1EDkTsf63Ub2C6O7GuYFDsSXUwsaZDurV0np41ocwq0jthUAYCmhBX9f+KwlaCgIuWyr/4WlUQUBfKfZog==",
       "dev": true
     },
+    "any-shell-escape": {
+      "version": "0.1.1",
+      "resolved": "https://registry.npmjs.org/any-shell-escape/-/any-shell-escape-0.1.1.tgz",
+      "integrity": "sha1-1Vq5ciRMcaml4asIefML8RCAaVk=",
+      "dev": true
+    },
     "anymatch": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/anymatch/-/anymatch-2.0.0.tgz",
@@ -3393,6 +3414,106 @@
         }
       }
     },
+    "concurrently": {
+      "version": "3.6.1",
+      "resolved": "https://registry.npmjs.org/concurrently/-/concurrently-3.6.1.tgz",
+      "integrity": "sha512-/+ugz+gwFSEfTGUxn0KHkY+19XPRTXR8+7oUK/HxgiN1n7FjeJmkrbSiXAJfyQ0zORgJYPaenmymwon51YXH9Q==",
+      "dev": true,
+      "requires": {
+        "chalk": "^2.4.1",
+        "commander": "2.6.0",
+        "date-fns": "^1.23.0",
+        "lodash": "^4.5.1",
+        "read-pkg": "^3.0.0",
+        "rx": "2.3.24",
+        "spawn-command": "^0.0.2-1",
+        "supports-color": "^3.2.3",
+        "tree-kill": "^1.1.0"
+      },
+      "dependencies": {
+        "commander": {
+          "version": "2.6.0",
+          "resolved": "https://registry.npmjs.org/commander/-/commander-2.6.0.tgz",
+          "integrity": "sha1-nfflL7Kgyw+4kFjugMMQQiXzfh0=",
+          "dev": true
+        },
+        "has-flag": {
+          "version": "1.0.0",
+          "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-1.0.0.tgz",
+          "integrity": "sha1-nZ55MWXOAXoA8AQYxD+UKnsdEfo=",
+          "dev": true
+        },
+        "load-json-file": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/load-json-file/-/load-json-file-4.0.0.tgz",
+          "integrity": "sha1-L19Fq5HjMhYjT9U62rZo607AmTs=",
+          "dev": true,
+          "requires": {
+            "graceful-fs": "^4.1.2",
+            "parse-json": "^4.0.0",
+            "pify": "^3.0.0",
+            "strip-bom": "^3.0.0"
+          }
+        },
+        "parse-json": {
+          "version": "4.0.0",
+          "resolved": "https://registry.npmjs.org/parse-json/-/parse-json-4.0.0.tgz",
+          "integrity": "sha1-vjX1Qlvh9/bHRxhPmKeIy5lHfuA=",
+          "dev": true,
+          "requires": {
+            "error-ex": "^1.3.1",
+            "json-parse-better-errors": "^1.0.1"
+          }
+        },
+        "path-type": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/path-type/-/path-type-3.0.0.tgz",
+          "integrity": "sha512-T2ZUsdZFHgA3u4e5PfPbjd7HDDpxPnQb5jN0SrDsjNSuVXHJqtwTnWqG0B1jZrgmJ/7lj1EmVIByWt1gxGkWvg==",
+          "dev": true,
+          "requires": {
+            "pify": "^3.0.0"
+          }
+        },
+        "pify": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/pify/-/pify-3.0.0.tgz",
+          "integrity": "sha1-5aSs0sEB/fPZpNB/DbxNtJ3SgXY=",
+          "dev": true
+        },
+        "read-pkg": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/read-pkg/-/read-pkg-3.0.0.tgz",
+          "integrity": "sha1-nLxoaXj+5l0WwA4rGcI3/Pbjg4k=",
+          "dev": true,
+          "requires": {
+            "load-json-file": "^4.0.0",
+            "normalize-package-data": "^2.3.2",
+            "path-type": "^3.0.0"
+          }
+        },
+        "rx": {
+          "version": "2.3.24",
+          "resolved": "https://registry.npmjs.org/rx/-/rx-2.3.24.tgz",
+          "integrity": "sha1-FPlQpCF9fjXapxu8vljv9o6ksrc=",
+          "dev": true
+        },
+        "strip-bom": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/strip-bom/-/strip-bom-3.0.0.tgz",
+          "integrity": "sha1-IzTBjpx1n3vdVv3vfprj1YjmjtM=",
+          "dev": true
+        },
+        "supports-color": {
+          "version": "3.2.3",
+          "resolved": "https://registry.npmjs.org/supports-color/-/supports-color-3.2.3.tgz",
+          "integrity": "sha1-ZawFBLOVQXHYpklGsq48u4pfVPY=",
+          "dev": true,
+          "requires": {
+            "has-flag": "^1.0.0"
+          }
+        }
+      }
+    },
     "condense-newlines": {
       "version": "0.2.1",
       "resolved": "https://registry.npmjs.org/condense-newlines/-/condense-newlines-0.2.1.tgz",
@@ -3654,6 +3775,83 @@
         }
       }
     },
+    "cpy": {
+      "version": "4.0.1",
+      "resolved": "https://registry.npmjs.org/cpy/-/cpy-4.0.1.tgz",
+      "integrity": "sha1-tnJn66LzlgugalphrJQDNCKDNCQ=",
+      "dev": true,
+      "requires": {
+        "cp-file": "^3.1.0",
+        "globby": "^4.0.0",
+        "meow": "^3.6.0",
+        "nested-error-stacks": "^1.0.0",
+        "object-assign": "^4.0.1",
+        "pinkie-promise": "^2.0.0"
+      },
+      "dependencies": {
+        "cp-file": {
+          "version": "3.2.0",
+          "resolved": "https://registry.npmjs.org/cp-file/-/cp-file-3.2.0.tgz",
+          "integrity": "sha1-b4NhYlRiTwrViqSqjQdvAmvn4Yg=",
+          "dev": true,
+          "requires": {
+            "graceful-fs": "^4.1.2",
+            "mkdirp": "^0.5.0",
+            "nested-error-stacks": "^1.0.1",
+            "object-assign": "^4.0.1",
+            "pify": "^2.3.0",
+            "pinkie-promise": "^2.0.0",
+            "readable-stream": "^2.1.4"
+          }
+        },
+        "glob": {
+          "version": "6.0.4",
+          "resolved": "https://registry.npmjs.org/glob/-/glob-6.0.4.tgz",
+          "integrity": "sha1-DwiGD2oVUSey+t1PnOJLGqtuTSI=",
+          "dev": true,
+          "requires": {
+            "inflight": "^1.0.4",
+            "inherits": "2",
+            "minimatch": "2 || 3",
+            "once": "^1.3.0",
+            "path-is-absolute": "^1.0.0"
+          }
+        },
+        "globby": {
+          "version": "4.1.0",
+          "resolved": "https://registry.npmjs.org/globby/-/globby-4.1.0.tgz",
+          "integrity": "sha1-CA9UVJ7BuCpsYOYx/ILhIR2+lfg=",
+          "dev": true,
+          "requires": {
+            "array-union": "^1.0.1",
+            "arrify": "^1.0.0",
+            "glob": "^6.0.1",
+            "object-assign": "^4.0.1",
+            "pify": "^2.0.0",
+            "pinkie-promise": "^2.0.0"
+          }
+        },
+        "nested-error-stacks": {
+          "version": "1.0.2",
+          "resolved": "https://registry.npmjs.org/nested-error-stacks/-/nested-error-stacks-1.0.2.tgz",
+          "integrity": "sha1-GfYZWRUZ8JZ2mlupqG5u7sgjw88=",
+          "dev": true,
+          "requires": {
+            "inherits": "~2.0.1"
+          }
+        }
+      }
+    },
+    "cpy-cli": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/cpy-cli/-/cpy-cli-1.0.1.tgz",
+      "integrity": "sha1-Z/taSi3sKMqKv/N13kuecfanVhw=",
+      "dev": true,
+      "requires": {
+        "cpy": "^4.0.0",
+        "meow": "^3.6.0"
+      }
+    },
     "create-ecdh": {
       "version": "4.0.3",
       "resolved": "https://registry.npmjs.org/create-ecdh/-/create-ecdh-4.0.3.tgz",
@@ -11307,6 +11505,12 @@
       "integrity": "sha1-Sr6/7tdUHywnrPspvbvRXI1bpPc=",
       "dev": true
     },
+    "ncp": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/ncp/-/ncp-2.0.0.tgz",
+      "integrity": "sha1-GVoh1sRuNh0vsSgbo4uR6d9727M=",
+      "dev": true
+    },
     "needle": {
       "version": "2.4.0",
       "resolved": "https://registry.npmjs.org/needle/-/needle-2.4.0.tgz",
@@ -11916,6 +12120,47 @@
         }
       }
     },
+    "nps-utils": {
+      "version": "1.7.0",
+      "resolved": "https://registry.npmjs.org/nps-utils/-/nps-utils-1.7.0.tgz",
+      "integrity": "sha512-wq/gUxTR3sgLYTLHlUKwMG2paUV3QdfwMj5aifWpQ60Vv9RQzA6pXDkwrAlMA8SNqoz8FwaGPc1X/7I+qjuYwg==",
+      "dev": true,
+      "requires": {
+        "any-shell-escape": "^0.1.1",
+        "common-tags": "^1.4.0",
+        "concurrently": "^3.4.0",
+        "cpy-cli": "^1.0.1",
+        "cross-env": "^3.1.4",
+        "is-windows": "^1.0.0",
+        "mkdirp": "^0.5.1",
+        "ncp": "2.0.0",
+        "opn-cli": "^3.1.0",
+        "rimraf": "^2.6.1"
+      },
+      "dependencies": {
+        "cross-env": {
+          "version": "3.2.4",
+          "resolved": "https://registry.npmjs.org/cross-env/-/cross-env-3.2.4.tgz",
+          "integrity": "sha1-ngWF8neGTtQhznVvgamA/w1piro=",
+          "dev": true,
+          "requires": {
+            "cross-spawn": "^5.1.0",
+            "is-windows": "^1.0.0"
+          }
+        },
+        "cross-spawn": {
+          "version": "5.1.0",
+          "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-5.1.0.tgz",
+          "integrity": "sha1-6L0O/uWPz/b4+UUQoKVUu/ojVEk=",
+          "dev": true,
+          "requires": {
+            "lru-cache": "^4.0.1",
+            "shebang-command": "^1.2.0",
+            "which": "^1.2.9"
+          }
+        }
+      }
+    },
     "nth-check": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/nth-check/-/nth-check-1.0.2.tgz",
@@ -12326,6 +12571,43 @@
         "is-wsl": "^1.1.0"
       }
     },
+    "opn-cli": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/opn-cli/-/opn-cli-3.1.0.tgz",
+      "integrity": "sha1-+BmubK4LQRvQFJuFYP5siK2tIPg=",
+      "dev": true,
+      "requires": {
+        "file-type": "^3.6.0",
+        "get-stdin": "^5.0.1",
+        "meow": "^3.7.0",
+        "opn": "^4.0.0",
+        "temp-write": "^2.1.0"
+      },
+      "dependencies": {
+        "file-type": {
+          "version": "3.9.0",
+          "resolved": "https://registry.npmjs.org/file-type/-/file-type-3.9.0.tgz",
+          "integrity": "sha1-JXoHg4TR24CHvESdEH1SpSZyuek=",
+          "dev": true
+        },
+        "get-stdin": {
+          "version": "5.0.1",
+          "resolved": "https://registry.npmjs.org/get-stdin/-/get-stdin-5.0.1.tgz",
+          "integrity": "sha1-Ei4WFZHiH/TFJTAwVpPyDmOTo5g=",
+          "dev": true
+        },
+        "opn": {
+          "version": "4.0.2",
+          "resolved": "https://registry.npmjs.org/opn/-/opn-4.0.2.tgz",
+          "integrity": "sha1-erwi5kTf9jsKltWrfyeQwPAavJU=",
+          "dev": true,
+          "requires": {
+            "object-assign": "^4.0.1",
+            "pinkie-promise": "^2.0.0"
+          }
+        }
+      }
+    },
     "optimist": {
       "version": "0.6.1",
       "resolved": "https://registry.npmjs.org/optimist/-/optimist-0.6.1.tgz",
@@ -16678,6 +16960,28 @@
       "integrity": "sha1-CnwOom06Oa+n4OvqnB/AvE2qAR0=",
       "dev": true
     },
+    "temp-write": {
+      "version": "2.1.0",
+      "resolved": "https://registry.npmjs.org/temp-write/-/temp-write-2.1.0.tgz",
+      "integrity": "sha1-WYkJGODvCdVIqqNC9L00CdhATpY=",
+      "dev": true,
+      "requires": {
+        "graceful-fs": "^4.1.2",
+        "mkdirp": "^0.5.0",
+        "os-tmpdir": "^1.0.0",
+        "pify": "^2.2.0",
+        "pinkie-promise": "^2.0.0",
+        "uuid": "^2.0.1"
+      },
+      "dependencies": {
+        "uuid": {
+          "version": "2.0.3",
+          "resolved": "https://registry.npmjs.org/uuid/-/uuid-2.0.3.tgz",
+          "integrity": "sha1-Z+LoY3lyFVMN/zGOW/nc6/1Hsho=",
+          "dev": true
+        }
+      }
+    },
     "tempfile": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/tempfile/-/tempfile-2.0.0.tgz",
@@ -17142,6 +17446,12 @@
       "integrity": "sha1-YdvC1Ttp/2CRoSoWj9fUMxB+QPE=",
       "dev": true
     },
+    "tree-kill": {
+      "version": "1.2.2",
+      "resolved": "https://registry.npmjs.org/tree-kill/-/tree-kill-1.2.2.tgz",
+      "integrity": "sha512-L0Orpi8qGpRG//Nd+H90vFB+3iHnue1zSSGmNOOCh1GLJ7rUKVwV2HvijphGQS2UmhUZewS9VgvxYIdgr+fG1A==",
+      "dev": true
+    },
     "trim": {
       "version": "0.0.1",
       "resolved": "https://registry.npmjs.org/trim/-/trim-0.0.1.tgz",
@@ -17263,9 +17573,9 @@
       "dev": true
     },
     "typescript": {
-      "version": "3.5.1",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.5.1.tgz",
-      "integrity": "sha512-64HkdiRv1yYZsSe4xC1WVgamNigVYjlssIoaH2HcZF0+ijsk5YK2g0G34w9wJkze8+5ow4STd22AynfO6ZYYLw==",
+      "version": "3.7.5",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.7.5.tgz",
+      "integrity": "sha512-/P5lkRXkWHNAbcJIiHPfRoKqyd7bsyCma1hZNUGfn20qm64T6ZBlrzprymeu918H+mB/0rIg2gGK/BXkhhYgBw==",
       "dev": true
     },
     "typescript-eslint-parser": {
diff --git a/package-scripts.js b/package-scripts.js
index 0e414e1542..0332947d66 100644
--- a/package-scripts.js
+++ b/package-scripts.js
@@ -23,8 +23,18 @@ function test(testName, mochaParams) {
 module.exports = {
   scripts: {
     build: {
-      script: `browserify -e browser-entry.js --plugin ./scripts/dedefine --ignore './lib/cli/*.js' --ignore 'chokidar' --ignore 'fs' --ignore 'glob' --ignore 'path' --ignore 'supports-color' -o mocha.js`,
-      description: 'Build browser bundle'
+      default: {
+        script: 'nps build.types build.browser',
+        description: 'Build'
+      },
+      types: {
+        script: 'tsc -p . || true', // swallowing until I finish fixing all semantic errors
+        description: 'Build type declarations'
+      },
+      browser: {
+        script: `browserify -e browser-entry.js --plugin ./scripts/dedefine --ignore './lib/cli/*.js' --ignore 'chokidar' --ignore 'fs' --ignore 'glob' --ignore 'path' --ignore 'supports-color' -o mocha.js`,
+        description: 'Build browser bundle'
+      }
     },
     lint: {
       default: {
@@ -64,7 +74,7 @@ module.exports = {
     },
     test: {
       default: {
-        script: 'nps lint test.node test.browser test.bundle',
+        script: 'nps lint test.node test.browser test.bundle test.types',
         description: 'Run all linters and all tests'
       },
       node: {
@@ -251,6 +261,10 @@ module.exports = {
           description: 'Run AMD bundle tests',
           hiddenFromHelp: true
         }
+      },
+      types: {
+        script: 'cd test/types && tsc -p .',
+        description: 'Test emitted type declarations.'
       }
     },
     coveralls: {
diff --git a/package.json b/package.json
index aa77237f94..117f54a3c4 100644
--- a/package.json
+++ b/package.json
@@ -521,6 +521,7 @@
     "mocha": "./bin/mocha",
     "_mocha": "./bin/_mocha"
   },
+  "types": "types",
   "directories": {
     "lib": "./lib",
     "test": "./test"
@@ -564,6 +565,8 @@
     "@11ty/eleventy": "^0.8.3",
     "@mocha/contributors": "^1.0.4",
     "@mocha/docdash": "^2.1.2",
+    "@types/node": "^13.1.7",
+    "@types/yargs": "^15.0.0",
     "acorn": "^7.0.0",
     "assetgraph-builder": "^6.10.1",
     "autoprefixer": "^9.6.0",
@@ -615,6 +618,7 @@
     "svgo": "^1.2.2",
     "through2": "^3.0.1",
     "to-vfile": "^5.0.3",
+    "typescript": "^3.7.5",
     "unexpected": "^10.40.2",
     "unexpected-eventemitter": "^1.1.3",
     "unexpected-sinon": "^10.11.2",
diff --git a/test/types/mocha-tests.ts b/test/types/mocha-tests.ts
new file mode 100644
index 0000000000..b21abb9ffd
--- /dev/null
+++ b/test/types/mocha-tests.ts
@@ -0,0 +1,1285 @@
+import {
+    after as importedAfter,
+    before as importedBefore,
+    afterEach as importedAfterEach,
+    beforeEach as importedBeforeEach,
+    describe as importedDescribe,
+    it as importedIt,
+    xit as importedXit
+} from 'mocha';
+
+import LocalMocha = require('mocha');
+
+// Warning!!
+// Don't refer node.d.ts!!
+// See #22510.
+(): number => setTimeout(() => 0, 0);
+
+declare let number: number;
+declare let boolean: boolean;
+declare let string: string;
+declare let stringOrUndefined: string | undefined;
+declare let any: any;
+
+// Use module augmentation to add a third-party interface or reporter
+declare module 'mocha' {
+    interface InterfaceContributions {
+        'third-party-interface': never;
+    }
+    interface ReporterContributions {
+        'third-party-reporter': never;
+    }
+}
+
+const thirdPartyInterface: Mocha.Interface = 'third-party-interface';
+const thirdPartyReporter: Mocha.Reporter = 'third-party-reporter';
+
+// Lazy tests of compatibility between imported and global functions; should be identical
+const _after: typeof after = importedAfter;
+const _after2: typeof importedAfter = after;
+const _before: typeof before = importedBefore;
+const _before2: typeof importedBefore = before;
+const _afterEach: typeof afterEach = importedAfterEach;
+const _afterEach2: typeof importedAfterEach = afterEach;
+const _beforeEach: typeof beforeEach = importedBeforeEach;
+const _beforeEach2: typeof importedBeforeEach = beforeEach;
+const _describe: typeof describe = importedDescribe;
+const _describe2: typeof importedDescribe = describe;
+const _it: typeof it = importedIt;
+const _it2: typeof importedIt = it;
+const _xit: typeof xit = importedXit;
+const _xit2: typeof importedXit = xit;
+
+function test_bdd_describe() {
+    // $ExpectType Suite
+    describe('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType Suite
+    describe.only('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType void | Suite
+    describe.skip('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+}
+
+function test_bdd_context() {
+    // $ExpectType Suite
+    context('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType Suite
+    context.only('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType void | Suite
+    context.skip('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+}
+
+function test_bdd_xdescribe() {
+    // $ExpectType void | Suite
+    xdescribe('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+}
+
+function test_bdd_xcontext() {
+    // $ExpectType void | Suite
+    xcontext('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+}
+
+function test_tdd_suite() {
+    // $ExpectType Suite
+    suite('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType Suite
+    suite.only('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+
+    // $ExpectType void | Suite
+    suite.skip('something', function() {
+        // $ExpectType Suite
+        this;
+    });
+}
+
+function test_qunit_suite() {
+    // $ExpectType Suite
+    suite('some context');
+
+    // $ExpectType Suite
+    suite.only('some context');
+}
+
+function test_bdd_it() {
+    // $ExpectType Test
+    it(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.only(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.only(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.only('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.only('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.skip(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.skip(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.skip('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    it.skip('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType void
+    it.retries(number);
+}
+
+function test_bdd_xit() {
+    // $ExpectType Test
+    xit(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xit(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xit('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xit('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_bdd_specify() {
+    // $ExpectType Test
+    specify(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.only(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.only(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.only('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.only('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.skip(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.skip(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.skip('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    specify.skip('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType void
+    specify.retries(number);
+}
+
+function test_bdd_xspecify() {
+    // $ExpectType Test
+    xspecify(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xspecify(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xspecify('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    xspecify('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_tdd_qunit_test() {
+    // $ExpectType Test
+    test(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.only(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.only(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.only('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.only('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.skip(function doesSomething(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.skip(async function doesSomething() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.skip('does something', function(done) {
+        // $ExpectType Done
+        done;
+
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType Test
+    test.skip('does something', async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    // $ExpectType void
+    test.retries(number);
+}
+
+function test_bdd_qunit_before() {
+    before(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    before(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    before('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    before('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_tdd_setup() {
+    setup(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    setup(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    setup('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    setup('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_bdd_qunit_after() {
+    after(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    after(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    after('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    after('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_tdd_teardown() {
+    teardown(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    teardown(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    teardown('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    teardown('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_bdd_qunit_beforeEach() {
+    beforeEach(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    beforeEach(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    beforeEach('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    beforeEach('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_tdd_suiteSetup() {
+    suiteSetup(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    suiteSetup(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    suiteSetup('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    suiteSetup('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_bdd_qunit_afterEach() {
+    afterEach(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    afterEach(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    afterEach('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    afterEach('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_tdd_suiteTeardown() {
+    suiteTeardown(function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    suiteTeardown(async function() {
+        // $ExpectType Context
+        this;
+    });
+
+    suiteTeardown('description', function(done) {
+        // $ExpectType Done
+        done;
+        // $ExpectType Context
+        this;
+    });
+
+    suiteTeardown('description', async function() {
+        // $ExpectType Context
+        this;
+    });
+}
+
+function test_Context(ctx: LocalMocha.Context, runnable: LocalMocha.Runnable) {
+    // $ExpectType never
+    ctx.skip(); // throws
+
+    // $ExpectType boolean
+    ctx.enableTimeouts();
+
+    // $ExpectType Context
+    ctx.enableTimeouts(boolean);
+
+    // $ExpectType number
+    ctx.retries();
+
+    // $ExpectType Context
+    ctx.retries(number);
+
+    // $ExpectType Runnable
+    ctx.runnable();
+
+    // $ExpectType Context
+    ctx.runnable(runnable);
+
+    // $ExpectType number
+    ctx.slow();
+
+    // $ExpectType Context
+    ctx.slow(number);
+
+    // $ExpectType number
+    ctx.timeout();
+
+    // $ExpectType Context
+    ctx.timeout(number);
+
+    // $ExpectType Test | undefined
+    ctx.currentTest;
+
+    // $ExpectType Runnable | undefined
+    ctx.test;
+
+    ctx["extended"] = any;
+
+    // $ExpectType any
+    ctx["extended"];
+
+    ctx.enableTimeouts(boolean)
+        .retries(number)
+        .runnable(runnable)
+        .slow(number)
+        .timeout(number)
+        .skip();
+}
+
+function test_reporter_string(localMocha: LocalMocha) {
+    // $ExpectType BrowserMocha
+    mocha.reporter('html');
+
+    const m: Mocha = localMocha.reporter('html');
+}
+
+function test_reporter_function(localMocha: LocalMocha) {
+    // $ExpectType BrowserMocha
+    mocha.reporter(class extends LocalMocha.reporters.Base { });
+
+    const m: Mocha = localMocha.reporter(class extends LocalMocha.reporters.Base { });
+}
+
+function test_browser_mocha_setup_slow_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ slow: 25 });
+}
+
+function test_browser_mocha_setup_timeout_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ timeout: 25 });
+}
+
+function test_browser_mocha_setup_globals_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ globals: ['mocha'] });
+}
+
+function test_browser_mocha_setup_ui_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ ui: 'bdd' });
+}
+
+function test_browser_mocha_setup_reporter_string_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ reporter: 'html' });
+}
+
+function test_browser_mocha_setup_require_stringArray_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ require: ['ts-node/register'] });
+}
+
+function test_browser_mocha_setup_reporter_function_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ reporter: class extends LocalMocha.reporters.Base { } });
+}
+
+function test_browser_mocha_setup_bail_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ bail: false });
+}
+
+function test_browser_mocha_setup_ignore_leaks_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ ignoreLeaks: false });
+}
+
+function test_browser_mocha_setup_grep_string_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ grep: "describe" });
+}
+
+function test_browser_mocha_setup_grep_regex_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ grep: new RegExp('describe') });
+}
+
+function test_browser_mocha_setup_grep_regex_literal_option() {
+    // $ExpectType BrowserMocha
+    mocha.setup({ grep: /(expect|should)/i });
+}
+
+function test_browser_mocha_setup_all_options() {
+    // $ExpectType BrowserMocha
+    mocha.setup({
+        slow: 25,
+        timeout: 25,
+        ui: 'bdd',
+        globals: ['mocha'],
+        reporter: 'html',
+        bail: true,
+        ignoreLeaks: true,
+        grep: 'test',
+        require: ['ts-node/register'] // TODO: It doesn't appear this is actually supported. Should it be removed?
+    });
+}
+
+function test_constructor_slow_option() {
+    const m: Mocha = new LocalMocha({ slow: 25 });
+}
+
+function test_constructor_timeout_option() {
+    const m: Mocha = new LocalMocha({ timeout: 25 });
+}
+
+function test_constructor_globals_option() {
+    const m: Mocha = new LocalMocha({ globals: ['mocha'] });
+}
+
+function test_constructor_ui_option() {
+    const m: Mocha = new LocalMocha({ ui: 'bdd' });
+}
+
+function test_constructor_reporter_string_option() {
+    const m: Mocha = new LocalMocha({ reporter: 'html' });
+}
+
+function test_constructor_reporter_function_option() {
+    const m: Mocha = new LocalMocha({ reporter: class extends LocalMocha.reporters.Base { } });
+}
+
+function test_constructor_bail_option() {
+    const m: Mocha = new LocalMocha({ bail: false });
+}
+
+function test_constructor_ignore_leaks_option() {
+    const m: Mocha = new LocalMocha({ ignoreLeaks: false });
+}
+
+function test_constructor_grep_string_option() {
+    const m: Mocha = new LocalMocha({ grep: "describe" });
+}
+
+function test_constructor_grep_regex_option() {
+    const m: Mocha = new LocalMocha({ grep: new RegExp('describe') });
+}
+
+function test_constructor_grep_regex_literal_option() {
+    const m: Mocha = new LocalMocha({ grep: /(expect|should)/i });
+}
+
+function test_constructor_all_options() {
+    const m: Mocha = new LocalMocha({
+        slow: 25,
+        timeout: 25,
+        ui: 'bdd',
+        globals: ['mocha'],
+        reporter: 'html',
+        bail: true,
+        ignoreLeaks: true,
+        grep: 'test'
+    });
+}
+
+function test_run(localMocha: LocalMocha) {
+    // $ExpectType Runner
+    mocha.run();
+
+    // $ExpectType Runner
+    mocha.run((failures) => {
+        // $ExpectType number
+        failures;
+    });
+
+    // $ExpectType Runner
+    localMocha.run();
+
+    // $ExpectType Runner
+    localMocha.run((failures) => {
+        // $ExpectType number
+        failures;
+    });
+}
+
+function test_growl() {
+    mocha.growl();
+}
+
+function test_chaining() {
+    new LocalMocha({ slow: 25 })
+        .growl()
+        .reporter('html')
+        .reporter(class extends LocalMocha.reporters.Base { });
+}
+
+function test_require_constructor_empty() {
+    const instance = new LocalMocha();
+}
+
+function test_require_constructor_noOptions() {
+    const instance = new LocalMocha({});
+}
+
+function test_require_constructor_allOptions() {
+    const instance = new LocalMocha({
+        grep: /[a-z]*/,
+        ui: 'tdd',
+        reporter: 'dot',
+        timeout: 500,
+        bail: true
+    });
+}
+
+function test_require_fluentParams() {
+    const instance = new LocalMocha();
+
+    instance.bail(true)
+        .bail()
+        .addFile('foo.js')
+        .reporter('dot')
+        .ui('bdd')
+        .grep('[a-z]*')
+        .grep(/[a-z]*/)
+        .invert()
+        .ignoreLeaks(true)
+        .checkLeaks()
+        .growl()
+        .globals('foo')
+        .globals(['bar', 'zap'])
+        .useColors(true)
+        .useInlineDiffs(true)
+        .timeout(500)
+        .slow(100)
+        .enableTimeouts(true)
+        .asyncOnly()
+        .noHighlighting()
+        .run();
+}
+
+function test_throwError() {
+    mocha.throwError(new Error("I'm an error!"));
+}
+
+function test_mochaRunner_properties(runner: LocalMocha.Runner, suite: LocalMocha.Suite) {
+    // $Expecttype Runner
+    runner.abort();
+
+    // $ExpectType Suite
+    runner.suite;
+
+    // $ExpectType boolean
+    runner.started;
+
+    // $ExpectType number
+    runner.total;
+
+    // $ExpectType number
+    runner.failures;
+
+    // $ExpectType Runner
+    runner.grep(/regex/, false);
+
+    // $ExpectType number
+    runner.grepTotal(suite);
+
+    // $ExpectType string[]
+    runner.globals();
+
+    // $ExpectType Runner
+    runner.globals(["hello", "world"]);
+
+    // $ExpectType Runner
+    runner.run();
+
+    // $ExpectType Runner
+    runner.run((failures) => {
+        // $ExpectType number
+        failures;
+    });
+}
+
+function test_base_reporter_properties(reporter: LocalMocha.reporters.Base) {
+    // $ExpectType number
+    reporter.stats.failures;
+
+    // $ExpectType number
+    reporter.stats.passes;
+
+    // $ExpectType number
+    reporter.stats.pending;
+
+    // $ExpectType number
+    reporter.stats.suites;
+
+    // $ExpectType number
+    reporter.stats.tests;
+
+    // $ExpectType Date | undefined
+    reporter.stats.start;
+
+    // $ExpectType Date | undefined
+    reporter.stats.end;
+
+    // $ExpectType number | undefined
+    reporter.stats.duration;
+}
+
+function test_runner_events(runner: LocalMocha.Runner) {
+    // $ExpectType Runner
+    runner.on("start", () => {});
+
+    // $ExpectType Runner
+    runner.on("end", () => {});
+
+    // $ExpectType Runner
+    runner.on("suite", (suite) => {
+        // $ExpectType Suite
+        suite;
+    });
+
+    // $ExpectType Runner
+    runner.on("suite end", (suite) => {
+        // $ExpectType Suite
+        suite;
+    });
+
+    // $ExpectType Runner
+    runner.on("test", (test) => {
+        // $ExpectType Test
+        test;
+    });
+
+    // $ExpectType Runner
+    runner.on("test end", (test) => {
+        // $ExpectType Test
+        test;
+    });
+
+    // $ExpectType Runner
+    runner.on("hook", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Runner
+    runner.on("hook end", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Runner
+    runner.on("pass", (test) => {
+        // $ExpectType Test
+        test;
+    });
+
+    // $ExpectType Runner
+    runner.on("fail", (test, err) => {
+        // $ExpectType Test
+        test;
+
+        // $ExpectType any
+        err;
+    });
+
+    // $ExpectType Runner
+    runner.on("pending", (test) => {
+        // $ExpectType Test
+        test;
+    });
+}
+
+function test_runnable_events(runnable: LocalMocha.Runnable) {
+    // $ExpectType Runnable
+    runnable.on("error", (error) => {
+        // $ExpectType any
+        error;
+    });
+}
+
+function test_suite_events(suite: LocalMocha.Suite) {
+    // $ExpectType Suite
+    suite.on("beforeAll", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Suite
+    suite.on("afterAll", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Suite
+    suite.on("beforeEach", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Suite
+    suite.on("afterEach", (hook) => {
+        // $ExpectType Hook
+        hook;
+    });
+
+    // $ExpectType Suite
+    suite.on("run", () => { });
+
+    // $ExpectType Suite
+    suite.on("pre-require", (context, file, mocha) => {
+        // $ExpectType MochaGlobals
+        context;
+        // $ExpectType string
+        file;
+        const m: Mocha = mocha;
+    });
+
+    // $ExpectType Suite
+    suite.on("require", (module, file, mocha) => {
+        // $ExpectType any
+        module;
+        // $ExpectType string
+        file;
+        const m: Mocha = mocha;
+    });
+
+    // $ExpectType Suite
+    suite.on("post-require", (context, file, mocha) => {
+        // $ExpectType MochaGlobals
+        context;
+        // $ExpectType string
+        file;
+        const m: Mocha = mocha;
+    });
+}
+
+function test_backcompat_Suite(suite: Mocha.Suite, iSuite: Mocha.ISuite, iSuiteContext: Mocha.ISuiteCallbackContext, iTest: Mocha.ITest, iContext: Mocha.IContext) {
+    iSuite = suite;
+    iSuiteContext = suite;
+    suite.addTest(iTest);
+    suite.addSuite(iSuite);
+    LocalMocha.Suite.create(iSuite, string);
+    new LocalMocha.Suite(string, iContext);
+}
+
+function test_backcompat_Runner(runner: Mocha.Runner, iRunner: Mocha.IRunner, iSuite: Mocha.ISuite) {
+    iRunner = runner;
+    runner.grepTotal(iSuite);
+}
+
+function test_backcompat_Runnable(runnable: Mocha.Runnable, iRunnable: Mocha.IRunnable) {
+    iRunnable = runnable;
+}
+
+function test_backcompat_Test(test: Mocha.Test, iTest: Mocha.ITest) {
+    iTest = test;
+}
+
+function test_backcompat_Hook(hook: Mocha.Hook, iHook: Mocha.IHook) {
+    iHook = hook;
+}
+
+function test_backcompat_Context(context: Mocha.Context, iContext: Mocha.IContext,
+    iHookContext: Mocha.IHookCallbackContext, iBeforeAfterContext: Mocha.IBeforeAndAfterContext,
+    iTestContext: Mocha.ITestCallbackContext, iRunnable: Mocha.IRunnable) {
+    iContext = context;
+    iHookContext = context;
+    iBeforeAfterContext = context;
+    iTestContext = context;
+    context.runnable(iRunnable);
+}
+
+function test_backcompat_Base(iRunner: Mocha.IRunner) {
+    new LocalMocha.reporters.Base(iRunner);
+}
+
+function test_backcompat_XUnit(iRunner: Mocha.IRunner) {
+    new LocalMocha.reporters.XUnit(iRunner);
+}
+
+function test_backcompat_Progress(iRunner: Mocha.IRunner) {
+    new LocalMocha.reporters.Progress(iRunner);
+}
+
+import common = require("mocha/lib/interfaces/common");
+
+function test_interfaces_common(suites: Mocha.Suite[], context: Mocha.MochaGlobals, localMocha: Mocha,
+    fn: Mocha.Func | Mocha.AsyncFunc, test: Mocha.Test) {
+    const funcs = common(suites, context, localMocha);
+    // $ExpectType CommonFunctions
+    funcs;
+
+    funcs.before(fn);
+    funcs.before(string, fn);
+    funcs.beforeEach(fn);
+    funcs.beforeEach(string, fn);
+    funcs.after(fn);
+    funcs.after(string, fn);
+    funcs.afterEach(fn);
+    funcs.afterEach(string, fn);
+
+    // $ExpectType Suite
+    funcs.suite.create({ title: string });
+    funcs.suite.create({ title: string, file: string, fn: () => {}, pending: boolean, isOnly: boolean });
+
+    // $ExpectType Suite
+    funcs.suite.only({ title: string });
+    funcs.suite.only({ title: string, file: string, fn: () => {}, pending: boolean, isOnly: boolean });
+
+    // $ExpectType Suite
+    funcs.suite.skip({ title: string });
+    funcs.suite.skip({ title: string, file: string, fn: () => {}, pending: boolean, isOnly: boolean });
+
+    // $ExpectType Test
+    funcs.test.only(mocha, test);
+    funcs.test.skip(string);
+    funcs.test.retries(number);
+}
+
+// mocha-typescript (https://www.npmjs.com/package/mocha-typescript/) augments
+// the mocha functions and enables them to work as test class decorators.
+declare module "mocha" {
+    interface SuiteFunction {
+        <TFunction extends Function>(target: TFunction): TFunction | void;
+    }
+    interface PendingSuiteFunction {
+        <TFunction extends Function>(target: TFunction): TFunction | void;
+    }
+    interface ExclusiveSuiteFunction {
+        <TFunction extends Function>(target: TFunction): TFunction | void;
+    }
+    interface TestFunction {
+        (target: Object, propertyKey: string | symbol): void;
+    }
+    interface PendingTestFunction {
+        (target: Object, propertyKey: string | symbol): void;
+    }
+    interface ExclusiveTestFunction {
+        (target: Object, propertyKey: string | symbol): void;
+    }
+}
+
+@suite
+class TestClass1 {
+    @test method1() {}
+    @test.only method2() {}
+    @test.skip method3() {}
+}
+
+@suite.skip
+class TestClass2 {
+}
+
+@suite.only
+class TestClass3 {
+}
+// end of augmentations used by mocha-typescript
diff --git a/test/types/tsconfig.json b/test/types/tsconfig.json
new file mode 100644
index 0000000000..5de3cfada1
--- /dev/null
+++ b/test/types/tsconfig.json
@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "noEmit": true
+  }
+}
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000000..63dc5da533
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,14 @@
+{
+  "include": ["src"],
+  "compilerOptions": {
+    "rootDir": "lib",
+    "declarationDir": "types",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "sourceMap": true,
+    "declarationMap": true,
+    "newLine": "lf"
+  }
+}