The Difference Between null and undefined in JavaScript

In JavaScript, both null and undefined represent nothing. The only difference between the two is that null is explicit while undefined is implicit.

When a variable has not been given a value, undefined is inferred. When null is set as the value we explicitly say that there is no value. When we don’t know there’s no value, undefined is used, and when we know there’s no value, null is used.

The two types are also not equal. Take the following as an example:

// This will equal to true
undefined == null

// But this won't
undefined === null

// That's because
typeof undefined  // will be "undefined"
typeof null       // will be "object"

// Hence this will be false as well
typeof undefined == typeof null

And why null is an object? I suggest checking out the below article to find out more:

The history of "typeof null"

50 JavaScript Interview QuestionsAnd their answers explainedHere are 50 JavaScript interview questions that often come up during a technical interview. In one place, one resource to learn from.Learn More

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Resources:

• The null type in JavaScript
• The undefined type in JavaScript