adds new wiki - JS-Strict-Mode.md

FreeCodeCamp · c703aef0da58f6ab9d7eb3e6ebe0ac7bafca5abe · rishipuri committed Mar 3, 2016 · Mar 3, 2016 · c703aef
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+# Strict Mode
+
+Strict Mode was introduced in ECMAScript 5 that allows you to place a program, or a function, in a “strict” operating context. This strict context prevents certain actions from being taken and throws more exceptions.
+
+Strict mode makes several changes to normal JavaScript semantics. 
+* First, strict mode eliminates some JavaScript silent errors by changing them to throw errors. 
+* Second, strict mode fixes mistakes that make it difficult for JavaScript engines to perform optimizations: strict mode code can sometimes be made to run faster than identical code that's not strict mode. 
+* Third, strict mode prohibits some syntax likely to be defined in future versions of ECMAScript.
+
+Strict mode code and non-strict mode code can coexist in a same script.
+
+    // Non-strict code...
+    
+    (function(){
+      "use strict";
+    
+      // Define your library strictly...
+    })();
+    
+    // Non-strict code... 
+
+### Invoking strict mode
+
+Strict mode applies to *entire scripts* or to *individual functions*.
+
+**Strict mode for scripts**
+
+    // Whole-script strict mode syntax
+    
+    "use strict";
+    var v = "Hi!  I'm a strict mode script!";
+
+**Strict mode for functions**
+
+    function strict(){
+      // Function-level strict mode syntax
+      
+      'use strict';
+      function nested() { return "And so am I!"; }
+      return "Hi!  I'm a strict mode function!  " + nested();
+    }
+
+    function notStrict() { return "I'm not strict."; }
+
+**Basically it helps you make fewer errors, by detecting things that could lead to breakage which are not detected normally (non-strict mode).**
+
+*For more information check out this [MDN page](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Strict_mode).*