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
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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
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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 >
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Output :
Supported browsers
- Chrome 85
- Edge 85
- Firefox 79
- Safari 14