Nullish Coalescing Assignment (??=) Operator in JavaScript

This is a new operator introduced by javascript. This operator is represented by x ??= y and it is called Logical nullish assignment operator. Only if the value of x is nullish then the value of y will be assigned to x that means if the value of x is null or undefined then the value of y will be assigned to x.

Let's discuss how this logical nullish assignment operator works. Firstly we all know that logical nullish assignment is represented as x ??= y, this is derived by two operators nullish coalescing operator and assignment operator we can also write it as x ?? (x = y). Now javascript checks the x first, if it is nullish then the value of y will be assigned to x.

Syntax :

x ??= y  // Means : x ?? (x = y)

Example 1 :

let x = 12; let y = null; let z = 13; // The value of x will become  // unchanged because x is not nullish. x ??= z; // The value of y will be  // changed because y is nullish. y ??= z; console.log(x) // 12 console.log(y) // 13 

Output :

12 13

Example 2 :

let x = {  name : "Ram" } // The value of name will remain // unchanged because x.name is not nullish x.name ??= "Shyam"; // There is no any property named age in object x . // So the value of x.age will be  // undefined and undefined means nullish. // that's why the value of age will be assigned. x.age ??= 18; console.log(x.name) // Ram console.log(x.age) // 18 

Output :

"Ram" 18

Example 3:

<h1>Hello Geeksforgeeks</h1> <p id="print_arr"></p> <script>  let arr = [1, 2, "apple", null, undefined, []]    // Replace each nullish values with "gfg"  arr.forEach((item, index)=>{  arr[index] ??= "gfg"  })    document.getElementById("print_arr")  .innerText = arr.toString();  //console.log(arr) </script> 

Output :

Supported browsers

• Chrome 85
• Edge 85
• Firefox 79
• Safari 14