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 :
Javascript
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 :
Javascript
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:
HTML
<h1>Hello Geeksforneveropen</h1> <p id="print_arr"></p> Â Â <script> Â Â Â Â let arr = [1, 2, "apple", null, undefined, []] Â Â Â Â Â Â Â Â Â Â // Replace each nullish values with "gfg" Â Â Â Â arr.forEach((item, index)=>{ Â Â Â Â Â Â arr[index] ??= "gfg" Â Â Â Â Â Â Â Â }) Â Â Â Â Â Â Â Â Â Â Â Â Â Â document.getElementById("print_arr") Â Â Â Â .innerText = arr.toString(); Â Â Â Â Â Â Â Â //console.log(arr) </script> |
Output :
Supported browsers
- Chrome 85
- Edge 85
- Firefox 79
- Safari 14
