In JavaScript, both undefined and null represent the absence of a meaningful value, but they have different purposes and are used in distinct contexts. Knowing when and how to use each can help you write clearer, more predictable code. Let's see the differences between undefined and null in JavaScript. What is undefined?

undefined is a global property with the value undefined . null is a global property with the value null . undefined values are omitted during serialization. null values are preserved during JSON serialization (e.g., {"key": null} ). undefined indicates a variable hasn’t been initialized, while null is intentionally assigned to indicate no value.

The undefined value is a primitive value used when a variable has not been assigned a value. The null value is a primitive value that represents the null, empty, or non-existent reference. When you declare a variable through var and do not give it a value, it will have the value undefined.

As typeof returns undefined, undefined is a type where as null is an initializer indicates the variable points to no object (virtually everything in Javascript is an object). null - It is an assignment value, which is used with variable to represent no value (it's an object).