[Easy] 📄 null & undefined

Key Differences

• undefined：
  • Indicates a variable has been declared but not assigned.
  • It is the default value for uninitialized variables.
  • A function returns undefined if no explicit return value is provided.
• null：
  • Represents an empty value or no value.
  • Usually assigned explicitly as null.
  • Used to indicate a variable intentionally points to nothing.

Example

let x;
console.log(x); // output: undefined

function foo() {}
console.log(foo()); // output: undefined

let y = null;
console.log(y); // output: null

let obj = { x: 5 };
obj.x = null;
console.log(obj.x); // output: null

Validation with typeof

console.log(typeof undefined); // output: "undefined"
console.log(typeof null); // output: "object"

console.log(null == undefined); // output: true
console.log(null === undefined); // output: false