What\'s the Difference Between Null and Undefined in JavaScript?

Understanding Null and Undefined in JavaScript

JavaScript, unlike most other programming languages, considers null an object. This distinction has implications for both its behavior and comparison with other values.

Why is null an Object?

While null is commonly used to represent the absence of a value, it's treated as an object in JavaScript due to historical reasons. In early versions of the language, there was no distinction between objects and primitive values. As a result, null was categorized as an object to avoid breaking compatibility with existing code.

null vs. undefined

The primary difference between null and undefined lies in their existence and purpose:

• undefined: Indicates that a variable has not been assigned or initialized with any value.
• null: Represents an intentional absence of a value; it's explicitly assigned to indicate that a variable doesn't have a value.

Comparison of if ( object == null ) vs. if ( !object )

The expressions if ( object == null ) and if ( !object ) are not equivalent in JavaScript.

• if ( object == null ): Checks if the variable object is either null or undefined. It returns true if either of those conditions is met.
• if ( !object ): Checks if the variable object is considered "falsy" in JavaScript. This includes null, undefined, 0, "", false, and objects that have no properties.

In most cases, checking for null specifically is more concise and appropriate. However, checking for "falsy" values using !object can be useful in certain scenarios.

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