Add eslint error checking w/ travis (#653)

.travis.yml

@@ -0,0 +1,6 @@
+language: node_js
+node_js:
+  - "6"
+
+script:
+  - npm run lint

index.js

@@ -344,7 +344,7 @@ function loginHelper(appState, email, password, globalOptions, callback) {
         .get("https://www.facebook.com/ajax/presence/reconnect.php", ctx.jar, form)
         .then(utils.saveCookies(ctx.jar));
     })
-    .then(function(res) {
+    .then(function(_res) {
       log.info("login", 'Request to pull 1');
       var form = {
         channel : 'p_' + ctx.userID,

package.json

@@ -4,6 +4,7 @@
   "description": "Facebook chat API that doesn't rely on XMPP.  Will NOT be deprecated April 30th 2015.",
   "scripts": {
     "test": "mocha",
+    "lint": "./node_modules/.bin/eslint **.js",
     "prettier": "prettier utils.js src/* --write"
   },
   "repository": {
@@ -31,6 +32,17 @@
   },
   "devDependencies": {
     "mocha": "^2.2.5",
-    "prettier": "^1.11.1"
+    "prettier": "^1.11.1",
+    "eslint": "^4.19.1"
+  },
+  "eslintConfig": {
+    "env": { "es6": true, "node": true },
+    "extends": "eslint:recommended",
+    "parserOptions": { "sourceType": "module" },
+    "rules": {
+        "linebreak-style": [ "error", "unix" ],
+        "semi": [ "error", "always" ],
+        "no-unused-vars": [1, {"argsIgnorePattern": "^_"}]
+    }
   }
 }

utils.js

@@ -1090,8 +1090,8 @@ function parseAndCheckLogin(ctx, defaultFuncs, retryCount) {
 
             // Update ttstamp since that depends on fb_dtsg
             ctx.ttstamp = "2";
-            for (var i = 0; i < ctx.fb_dtsg.length; i++) {
-              ctx.ttstamp += ctx.fb_dtsg.charCodeAt(i);
+            for (var j = 0; j < ctx.fb_dtsg.length; j++) {
+              ctx.ttstamp += ctx.fb_dtsg.charCodeAt(j);
             }
           }
         }