In JavaScript, what will 'typeof null' return?

Understanding The 'typeof' Operator and Null Values in JavaScript

JavaScript has an operator called typeof that is used to identify the data type of a value. When you use it with null, it doesn't respond like one might expect. That is, when you try to find the data type of a null value, JavaScript returns 'object' instead of 'null'.

Let's look at a small example to understand this concept:

var value = null;
console.log(typeof value);  // Output: 'object'

In this example, we declare a variable value and assign the null value to it. When we subsequently inquire the type of the variable value using the typeof operator, we get an output of 'object'. This is an unusual behavior, considering that null is generally used to represent a non-existing or invalid object or address.

This idiosyncrasy in JavaScript comes from its initial implementation where data types were represented by a pair of bits, with the binary pattern for null being all zeros. The definition for the typeof operator was also designed in a way that undefined and unallocated values, which were represented as null, were considered as type object.

This leads to a small pitfall, as you can't reliably use typeof to check if a value is null. If you need to check for null, it's better to use strict equality (=== or !==).

var value = null;
if (value === null) {
   console.log('Value is null');

In this code, we're not asking JavaScript what the type of value is, but instead, we're comparing value directly to null. This method circumvents JavaScript's quirkiest behavior and gives us the result we want.

To sum up, typeof null in JavaScript will return 'object'. Remember this peculiarity when working with JavaScript, especially in situations where you need to check if a value is null. For precise checks, use strict equality instead of typeof.

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