diff --git a/assets/.eslintrc.json b/assets/.eslintrc.json
index f3829a49..089dced4 100644
--- a/assets/.eslintrc.json
+++ b/assets/.eslintrc.json
@@ -2,18 +2,22 @@
   "root": true,
   "extends": "eslint-config-airbnb-base/legacy",
   "rules": {
-    "camelcase": "off",
+    "camelcase": [
+      "error",
+      {
+        "allow": [
+          "^gcaptcha_"
+        ]
+      }
+    ],
     "consistent-return": "off",
-    "eqeqeq": "off",
     "func-names": "off",
-    "guard-for-in": "off",
     "max-len": "off",
     "no-bitwise": "off",
     "no-continue": "off",
     "no-multi-assign": "off",
     "no-param-reassign": "off",
     "no-plusplus": "off",
-    "no-prototype-builtins": "off",
     "no-restricted-syntax": "off",
     "no-shadow": "off",
     "no-use-before-define": "off",
diff --git a/assets/badge.js b/assets/badge.js
index 95d2321e..980f622b 100644
--- a/assets/badge.js
+++ b/assets/badge.js
@@ -56,9 +56,9 @@
     parent.removeChild(script)
 
     // setup iframe RPC
-    iframe.onload = function () {
+    iframe.addEventListener('load', function () {
       setup(iframe)
-    }
+    })
   }
 
   // setup an "RPC" channel between iframe and us
@@ -75,8 +75,8 @@
 
       // update width
       var wp = 'slackin-width:' + id + ':'
-      if (wp === e.data.substr(0, wp.length)) {
-        var width = e.data.substr(wp.length)
+      if (wp === e.data.slice(0, wp.length)) {
+        var width = e.data.slice(wp.length)
         iframe.style.width = width + 'px'
 
         // ensure it's shown (since first time hidden)
@@ -85,8 +85,8 @@
 
       // redirect to URL
       var redir = 'slackin-redirect:' + id + ':'
-      if (redir === e.data.substr(0, redir.length)) {
-        window.location.href = e.data.substr(redir.length) // lgtm [js/client-side-unvalidated-url-redirection]
+      if (redir === e.data.slice(0, redir.length)) {
+        window.location.href = e.data.slice(redir.length) // lgtm [js/client-side-unvalidated-url-redirection]
       }
     })
   }
@@ -133,12 +133,12 @@
     ni.style.height = '15.5em'
     ni.style.borderWidth = 0
     ni.src = iframe.src.replace('iframe', 'iframe/dialog')
-    ni.onload = function () {
+    ni.addEventListener('load', function () {
       setup(ni)
       window.addEventListener('scroll', dposition)
       window.addEventListener('resize', dposition)
       position()
-    }
+    })
 
     // arrows
     var a1 = document.createElement('div')
@@ -235,7 +235,7 @@
     }
 
     function click(ev) {
-      if (ev.target.className != '__slackin') {
+      if (ev.target.className !== '__slackin') {
         hide()
       }
     }
diff --git a/assets/client.js b/assets/client.js
index 4ec5ad0d..45848726 100644
--- a/assets/client.js
+++ b/assets/client.js
@@ -70,14 +70,18 @@ url.href = window.location
 // realtime updates
 var socket = io({ path: data.path + 'socket.io' })
 socket.on('data', function (users) {
-  for (var i in users) update(i, users[i])
+  for (var i in users) {
+    if (Object.prototype.hasOwnProperty.call(users, i)) {
+      update(i, users[i])
+    }
+  }
 })
 socket.on('total', function (n) { update('total', n) })
 socket.on('active', function (n) { update('active', n) })
 
 function update(val, n) {
   var el = document.querySelector('.' + val)
-  if (el && el.textContent != n) {
+  if (el && el.textContent !== n) {
     el.textContent = n
     anim(el, val)
   }
@@ -112,8 +116,8 @@ window.addEventListener('message', function onmsg(e) {
   }
 })
 
-body.onload = function () {
+body.addEventListener('load', function () {
   if (window.location.hash) {
     body.querySelector('select[name=channel]').value = window.location.hash.slice(1)
   }
-}
+})
diff --git a/assets/iframe.js b/assets/iframe.js
index 144ac2ff..58f2492c 100644
--- a/assets/iframe.js
+++ b/assets/iframe.js
@@ -19,7 +19,7 @@
       id = e.data.replace(/^slackin:/, '')
       document.body.addEventListener('click', function (ev) {
         var el = ev.target
-        while (el && el.nodeName != 'A') el = el.parentNode
+        while (el && el.nodeName !== 'A') el = el.parentNode
         if (el && el.target === '_blank') {
           ev.preventDefault()
           window.parent.postMessage('slackin-click:' + id, '*')
@@ -36,7 +36,7 @@
   var button = document.querySelector('.slack-button')
   var lastWidth
   function refresh() {
-    if (window != window.top && window.postMessage) {
+    if (window !== window.top && window.postMessage) {
       var width = Math.ceil(button.getBoundingClientRect().width)
       if (lastWidth !== width) {
         lastWidth = width
@@ -48,7 +48,7 @@
   // initialize realtime events asynchronously
   var script = document.createElement('script')
   script.src = 'https://cdnjs.cloudflare.com/ajax/libs/socket.io/1.7.4/socket.io.slim.min.js'
-  script.onload = function () {
+  script.addEventListener('load', function () {
     // use dom element for better cross browser compatibility
     var url = document.createElement('a')
     url.href = window.location
@@ -56,14 +56,18 @@
     var count = document.querySelector('.slack-count')
 
     socket.on('data', function (users) {
-      for (var i in users) update(i, users[i])
+      for (var i in users) {
+        if (Object.prototype.hasOwnProperty.call(users, i)) {
+          update(i, users[i])
+        }
+      }
     })
     socket.on('total', function (n) { update('total', n) })
     socket.on('active', function (n) { update('active', n) })
 
     var anim
     function update(key, n) {
-      if (data[key] != n) {
+      if (data[key] !== n) {
         data[key] = n
         var str = ''
         if (data.active) str = data.active + '/'
@@ -78,6 +82,6 @@
         refresh()
       }
     }
-  }
+  })
   document.body.appendChild(script)
 }())
diff --git a/lib/index.js b/lib/index.js
index 136c155c..91c882b5 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -64,7 +64,7 @@ function slackin({
   let channelsFiltered;
   if (channels) {
     channelsFiltered = channels.split(',').map((channel) => (
-      channel.startsWith('#') ? channel.substr(1) : channel
+      channel.startsWith('#') ? channel.slice(1) : channel
     ));
   }