Why Are Null and Undefined Different in JavaScript, and How Do You Check for Them?

Why is null an object?

In JavaScript, null is considered an object because it is a primitive value that has no properties or methods. This makes it different from other primitive values, such as strings, numbers, and booleans, which all have their own set of properties and methods.

Is checking if ( object == null ) the same as if ( !object ) ?

No, the checks if ( object == null ) and if ( !object ) are not the same. The == operator checks for equality, while the ! operator checks for truthiness. A truthy value is one that is not undefined, null, NaN, 0, false, or an empty string. Therefore, the check if ( !object ) will return true if object is undefined, null, or false, while the check if ( object == null ) will only return true if object is null.

What is the difference between null and undefined?

Null and undefined are both primitive values that represent the absence of a value. However, the difference between them is that null is a deliberate assignment of no value, while undefined is unintentionally absent from the program. Null is used to explicitly set a value to no value, indicating that the value is intentionally absent or unknown. Undefined generally indicates that the value was never declared or initialized in the program, or is not yet available.

The above is the detailed content of Why Are Null and Undefined Different in JavaScript, and How Do You Check for Them?. For more information, please follow other related articles on the PHP Chinese website!