feat: add expected erro class and its handling

Author: saintsebastian

bin/create-webextension

@@ -1,5 +1,8 @@
 #!/usr/bin/env node
 const chalk = require("chalk");
+const UsageError = require("../errors").UsageError;
+const onlyInstancesOf = require("../errors").onlyInstancesOf;
+
 
 const USAGE_MSG = `Usage: create-webextension project_dir_name`;
 
@@ -11,4 +14,7 @@ if (!process.argv[2]) {
 
 require("..").main(process.argv[2])
   .then(console.log)
-  .catch(err => console.log(err.message));
+  .catch(onlyInstancesOf(UsageError, (error) => {
+    console.log(`${chalk.red(error.message)}\n`);
+    process.exit(1);
+  }));

errors.js

@@ -0,0 +1,18 @@
+const ES6Error = require("es6-error");
+
+exports.onlyInstancesOf = function(errorType, handler) {
+  return(error) => {
+    if (error instanceof errorType) {
+      return handler(error);
+    } else {
+      console.log(error.stack);
+      process.exit(1);
+    }
+  }
+}
+
+exports.UsageError = class UsageError extends ES6Error {
+  constructor(message) {
+    super(message);
+  }
+}

index.js

@@ -4,6 +4,7 @@ const path = require("path");
 const chalk = require("chalk");
 const fs = require("mz/fs");
 const stripAnsi = require("strip-ansi");
+const UsageError = require("./errors").UsageError;
 
 const README = `
 This project contains a blank WebExtension addon, a "white canvas" for your new experiment of
@@ -110,7 +111,7 @@ exports.main = function main(dirPath) {
   }, error => {
     if (error.code === "EEXIST") {
       const msg = `Unable to create a new WebExtension: ${chalk.bold.underline(projectPath)} dir already exist.`;
-      throw new Error(msg);
+      throw new UsageError(msg);
     }
   }).catch((error) => {
     throw error;

package.json

@@ -33,6 +33,7 @@
   "homepage": "https://github.com/rpl/create-webextension#readme",
   "dependencies": {
     "chalk": "^1.1.3",
+    "es6-error": "^4.0.2",
     "mz": "^2.6.0",
     "strip-ansi": "^3.0.1"
   },