Add eslint and fix lint errors

polyfill/.eslintrc

@@ -0,0 +1,45 @@
+{
+  "env": {
+    "browser": true,
+    "node": true,
+    "mocha": true
+  },
+  "globals": {
+    "expect": false,
+    "sinon": false
+  },
+  "extends": [
+    "eslint:recommended"
+  ],
+  "rules": {
+    // possible errors
+    "no-cond-assign": 0,
+    "no-empty": 0,
+    "valid-jsdoc": [2, {
+      "prefer": {"return": "return"},
+      "requireReturn": false
+    }],
+    // best practices
+    "no-extra-bind": 2,
+    // style
+    "comma-spacing": [2, {"before": false, "after": true}],
+    "eol-last": [0],
+    "key-spacing": [2, {"beforeColon": false, "afterColon": true}],
+    "linebreak-style": [2, "unix"],
+    "max-len": [2, 80, {"ignoreUrls": true}],
+    "no-multiple-empty-lines": [2, {"max": 2}],
+    "no-unused-vars": ["error", {"vars": "all"}],
+    "no-trailing-spaces": 2,
+    "object-curly-spacing": [2, "never"],
+    "quotes": [2, "single"],
+    "require-jsdoc": [2, {
+      "require": {
+        "FunctionDeclaration": true,
+        "MethodDefinition": true,
+        "ClassDeclaration": true
+      }
+    }],
+    "semi": [2, "always"],
+    "semi-spacing": [2, {"before": false, "after": true}],
+  }
+}

polyfill/intersection-observer.js

@@ -45,7 +45,7 @@ function IntersectionObserverEntry(entry) {
   var intersectionRect = this.intersectionRect;
   var intersectionArea = intersectionRect.width * intersectionRect.height;
   this.intersectionRatio = targetArea ? (intersectionArea / targetArea) : 0;
-};
+}
 
 
 /**
@@ -85,7 +85,7 @@ function IntersectionObserver(callback, opt_options) {
   this.rootMargin = this._rootMarginValues.map(function(margin) {
     return margin.value + margin.unit;
   }).join(' ');
-};
+}
 
 
 /**
@@ -324,8 +324,6 @@ IntersectionObserver.prototype._checkForIntersections = function() {
 };
 
 
-
-
 /**
  * Accepts a target and root rect computes the intersection between then
  * following the algorithm in the spec.
@@ -607,7 +605,7 @@ function getBoundingClientRect(el) {
       left: rect.left,
       width: rect.right - rect.left,
       height: rect.bottom - rect.top
-    }
+    };
   }
   return rect;
 }