What is the difference between null and undefined in JavaScript?

Question

I want to know what the difference is between null and undefined in JavaScript.

Answer 1

In addition to a different meaning there are other differences:

1. Object destructuring works differently for these two values:

   const { a = "default" } = { a: undefined }; // a is "default"
   const { b = "default" } = { b: null };      // b is null
   

2. JSON.stringify() keeps null but omits undefined

   const json = JSON.stringify({ undefinedValue: undefined, nullValue: null });
   console.log(json); // prints {"nullValue":null}
   

3. typeof operator

   console.log(typeof undefined); // "undefined"
   console.log(typeof null);      // "object" instead of "null"