Added JSHint eqeqeq option article

Author: James Allardice

option-articles/eqeqeq-jshint.md

@@ -0,0 +1,71 @@
+<!---
+{
+    "titles": [
+        "eqeqeq"
+    ],
+    "slugs": [
+        "option-jshint-eqeqeq"
+    ],
+    "linters": [
+        "jshint"
+    ],
+    "author": "jallardice",
+    "subject": "option"
+}
+-->
+
+### What does this option do?
+
+The JSHint `eqeqeq` option is used to prohibit the use of the equals operator
+`==` and the does-not-equal operator `!=`. This enforces the use of the strict
+equality operators (`===` and `!==` instead). The strict equality operators
+differ from their non-strict counterparts by first comparing the type of each
+operand, rather than attempting to coerce them to a common type. In the
+following example we make use of the non-strict equality operator to check
+whether a value is either `null` or `undefined`:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+/*jshint eqeqeq: true */
+var x;
+if (x == null) {
+    // This will execute if x is null or undefined
+    doSomething();
+}
+```
+
+### When should I use this option?
+
+The use of the `eqeqeq` JSHint option will cause an "Expected '===' and instead
+saw '=='" error any time it encounters an equals or does-not-equal operator. As
+demonstrated in the above example these operators can be used in some situations
+to produce shorter code. However, their use can lead to bugs and unexpected
+behaviour. For that reason it's generally considered best practice to use the
+strict equality operators wherever possible. The example above can be written as
+follows instead:
+
+<!---
+{
+    "linter": "jshint"
+}
+-->
+```javascript
+/*jshint eqeqeq: true */
+var x;
+if (typeof x === "undefined" || x === null) {
+    // This will execute if x is null or undefined
+    doSomething();
+}
+```
+
+Note that this is an *enforcing* option which means JSHint does not apply it by
+default. If you do not explicitly set this option to `true` JSHint will allow
+the use of non-strict equality operators anywhere in your code.
+
+#### Recommendation
+
+Set this option to `true` (enforces the use of strict equality operators).