Adding Code Climate and fixing a few things it found

.codeclimate.yml

+---
+engines:
+  eslint:
+    enabled: true
+  duplication:
+    enabled: false
+    config:
+      languages:
+        - javascript
+
+exclude_paths:
+  - tests/
+  - dist/
+
+...
+
+/* vim: set expandtab shiftwidth=2 softtabstop=2: */

.eslintignore

+**/*{.,-}min.js
+tests/

.eslintrc

+ecmaFeatures:
+  modules: true
+  jsx: true
+
+env:
+  amd: true
+  browser: true
+  es6: true
+  jquery: true
+  node: true
+
+# http://eslint.org/docs/rules/
+rules:
+  # Possible Errors
+  comma-dangle: [2, never]
+  no-cond-assign: 2
+  no-console: 0
+  no-constant-condition: 2
+  no-control-regex: 2
+  no-debugger: 2
+  no-dupe-args: 2
+  no-dupe-keys: 2
+  no-duplicate-case: 2
+  no-empty: 2
+  no-empty-character-class: 2
+  no-ex-assign: 2
+  no-extra-boolean-cast: 2
+  no-extra-parens: 0
+  no-extra-semi: 2
+  no-func-assign: 2
+  no-inner-declarations: [2, functions]
+  no-invalid-regexp: 2
+  no-irregular-whitespace: 2
+  no-negated-in-lhs: 2
+  no-obj-calls: 2
+  no-regex-spaces: 2
+  no-sparse-arrays: 2
+  no-unexpected-multiline: 2
+  no-unreachable: 2
+  use-isnan: 2
+  valid-jsdoc: 0
+  valid-typeof: 2
+
+  # Best Practices
+  accessor-pairs: 2
+  block-scoped-var: 0
+  complexity: [2, 6]
+  consistent-return: 0
+  curly: 0
+  default-case: 0
+  dot-location: 0
+  dot-notation: 0
+  eqeqeq: 2
+  guard-for-in: 2
+  no-alert: 2
+  no-caller: 2
+  no-case-declarations: 2
+  no-div-regex: 2
+  no-else-return: 0
+  no-empty-label: 2
+  no-empty-pattern: 2
+  no-eq-null: 2
+  no-eval: 2
+  no-extend-native: 2
+  no-extra-bind: 2
+  no-fallthrough: 2
+  no-floating-decimal: 0
+  no-implicit-coercion: 0
+  no-implied-eval: 2
+  no-invalid-this: 0
+  no-iterator: 2
+  no-labels: 0
+  no-lone-blocks: 2
+  no-loop-func: 2
+  no-magic-number: 0
+  no-multi-spaces: 0
+  no-multi-str: 0
+  no-native-reassign: 2
+  no-new-func: 2
+  no-new-wrappers: 2
+  no-new: 2
+  no-octal-escape: 2
+  no-octal: 2
+  no-proto: 2
+  no-redeclare: 2
+  no-return-assign: 2
+  no-script-url: 2
+  no-self-compare: 2
+  no-sequences: 0
+  no-throw-literal: 0
+  no-unused-expressions: 2
+  no-useless-call: 2
+  no-useless-concat: 2
+  no-void: 2
+  no-warning-comments: 0
+  no-with: 2
+  radix: 2
+  vars-on-top: 0
+  wrap-iife: 2
+  yoda: 0
+
+  # Strict
+  strict: 0
+
+  # Variables
+  init-declarations: 0
+  no-catch-shadow: 2
+  no-delete-var: 2
+  no-label-var: 2
+  no-shadow-restricted-names: 2
+  no-shadow: 0
+  no-undef-init: 2
+  no-undef: 0
+  no-undefined: 0
+  no-unused-vars: 0
+  no-use-before-define: 0
+
+  # Node.js and CommonJS
+  callback-return: 2
+  global-require: 2
+  handle-callback-err: 2
+  no-mixed-requires: 0
+  no-new-require: 0
+  no-path-concat: 2
+  no-process-exit: 2
+  no-restricted-modules: 0
+  no-sync: 0
+
+  # Stylistic Issues
+  array-bracket-spacing: 0
+  block-spacing: 0
+  brace-style: 0
+  camelcase: 0
+  comma-spacing: 0
+  comma-style: 0
+  computed-property-spacing: 0
+  consistent-this: 0
+  eol-last: 0
+  func-names: 0
+  func-style: 0
+  id-length: 0
+  id-match: 0
+  indent: 0
+  jsx-quotes: 0
+  key-spacing: 0
+  linebreak-style: 0
+  lines-around-comment: 0
+  max-depth: 0
+  max-len: 0
+  max-nested-callbacks: 0
+  max-params: 0
+  max-statements: [2, 30]
+  new-cap: 0
+  new-parens: 0
+  newline-after-var: 0
+  no-array-constructor: 0
+  no-bitwise: 0
+  no-continue: 0
+  no-inline-comments: 0
+  no-lonely-if: 0
+  no-mixed-spaces-and-tabs: 0
+  no-multiple-empty-lines: 0
+  no-negated-condition: 0
+  no-nested-ternary: 0
+  no-new-object: 0
+  no-plusplus: 0
+  no-restricted-syntax: 0
+  no-spaced-func: 0
+  no-ternary: 0
+  no-trailing-spaces: 0
+  no-underscore-dangle: 0
+  no-unneeded-ternary: 0
+  object-curly-spacing: 0
+  one-var: 0
+  operator-assignment: 0
+  operator-linebreak: 0
+  padded-blocks: 0
+  quote-props: 0
+  quotes: 0
+  require-jsdoc: 0
+  semi-spacing: 0
+  semi: 0
+  sort-vars: 0
+  space-after-keywords: 0
+  space-before-blocks: 0
+  space-before-function-paren: 0
+  space-before-keywords: 0
+  space-in-parens: 0
+  space-infix-ops: 0
+  space-return-throw-case: 0
+  space-unary-ops: 0
+  spaced-comment: 0
+  wrap-regex: 0
+
+  # ECMAScript 6
+  arrow-body-style: 0
+  arrow-parens: 0
+  arrow-spacing: 0
+  constructor-super: 0
+  generator-star-spacing: 0
+  no-arrow-condition: 0
+  no-class-assign: 0
+  no-const-assign: 0
+  no-dupe-class-members: 0
+  no-this-before-super: 0
+  no-var: 0
+  object-shorthand: 0
+  prefer-arrow-callback: 0
+  prefer-const: 0
+  prefer-reflect: 0
+  prefer-spread: 0
+  prefer-template: 0
+  require-yield: 0

src/BasicSet.js

@@ -86,7 +86,9 @@ BasicSet.prototype.hasAll = function() {
 BasicSet.prototype.getAll = function() {
     var results = [];
     for (var key in this._data) {
-        results.push(this._data[key]);
+        if (this._data.hasOwnProperty(key)) {
+            results.push(this._data[key]);
+        }
     }
     return results;
 };
@@ -111,7 +113,9 @@ BasicSet.prototype.getIntersection = function(otherSet) {
 BasicSet.prototype.size = function() {
     var count = 0;
     for (var key in this._data) {
-        count++;
+        if (this._data.hasOwnProperty(key)) {
+            count++;
+        }
     }
     return count;
 };
@@ -123,7 +127,9 @@ BasicSet.prototype.size = function() {
  */
 BasicSet.prototype.isEmpty = function() {
     for (var key in this._data) {
-        return false;
+        if (this._data.hasOwnProperty(key)) {
+            return false;
+        }
     }
     return true;
 };