type of null

Author: rohan-paul

Javascript/Tricky-JS-Problems/Collection-of-Tricky-JS-Questlions.md

@@ -106,7 +106,7 @@
 
 ### Explanation
 
-> If `null` is a primitive, why does `typeof(null)` return `"object"`?
+If `null` is a primitive, why does `typeof(null)` return `"object"`?
 
 Because [the spec says so](http://www.ecma-international.org/ecma-262/5.1/#sec-11.4.3).
 

Javascript/Tricky-JS-Problems/typeof-null-why-its-object.md

@@ -0,0 +1,49 @@
+### If null is a primitive, why does typeof(null) return "object"?
+
+##### Explanation-1
+
+If `null` is a primitive, why does `typeof(null)` return `"object"`?
+
+Because [the spec says so](http://www.ecma-international.org/ecma-262/5.1/#sec-11.4.3).
+
+### [11.4.3][1] The `typeof` Operator
+
+The production _UnaryExpression_ : `typeof` _UnaryExpression_ is evaluated as follows:
+
+1.  Let _val_ be the result of evaluating _UnaryExpression_.
+2.  If [Type][2](_val_) is [Reference][3], then
+       a. If [IsUnresolvableReference][4](_val_) is **true**, return "**`undefined`**".
+       b. Let _val_ be [GetValue][5](_val_).
+3.  Return a String determined by [Type][6](_val_) according to Table 20.
+
+![enter image description here][7]
+
+[1]: http://www.ecma-international.org/ecma-262/5.1/#sec-11.4.3
+[2]: http://www.ecma-international.org/ecma-262/5.1/#sec-8
+[3]: http://www.ecma-international.org/ecma-262/5.1/#sec-8.7
+[4]: http://www.ecma-international.org/ecma-262/5.1/#sec-8.7
+[5]: http://www.ecma-international.org/ecma-262/5.1/#sec-8.7.1
+[6]: http://www.ecma-international.org/ecma-262/5.1/#sec-8
+[7]: http://i.stack.imgur.com/FzI1R.png
+
+---
+
+##### Explanation-2
+
+From [the MDN page about the behaviour of the `typeof` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof):
+
+<blockquote>
+<h3><code>null</code></h3>
+
+<pre>// This stands since the beginning of JavaScript
+typeof null === 'object';
+</pre>
+
+<p>In the first implementation of JavaScript, JavaScript values were represented as a type tag and a value. The type tag for objects was 0. <code>null</code> was represented as the NULL pointer (0x00 in most platforms). Consequently, null had 0 as type tag, hence the "object" <code>typeof</code> return value. (<a href="http://www.2ality.com/2013/10/typeof-null.html">reference</a>)</p>
+
+<p>A fix was proposed for ECMAScript (via an opt-in), but <a href="https://web.archive.org/web/20160331031419/http://wiki.ecmascript.org:80/doku.php?id=harmony:typeof_null">was rejected</a>. It would have resulted in <code>typeof null === 'null'</code>.</p>
+</blockquote>
+
+[1]: http://wiki.ecmascript.org/doku.php?id=harmony:typeof_null
+
+---