JAVASCRIPT

double question mark javascript

Nullish coalescing operator (??)
returns its right-hand side operand when its left-hand side operand is null or undefined, 
and otherwise returns its left-hand side operand.
const foo = null ?? 'default string';
console.log(foo);
// expected output: "default string" because left hand side is null.

const baz = 0 ?? 42;
console.log(baz);
// expected output: 0 , because left hand side ( 0 )  is not null or undefinded.

double question mark javascript

//Similar to || but only returns the right-hand operand if the left-hand is null or undefined
0 ?? "other" // 0
false ?? "other" // false
null ?? "other" // "other"
undefined ?? "other" // "other"

javascript double question mark

let a = null;
const b = a ?? -1;		// Same as b = ( a != null ? a : -1 );
console.log(b);		  	// output: -1
//OR IF
let a = 9;
const b = a ?? -1;
console.log(b);  		// output: 9

//PS.,VERY CLOSE TO '||' OPERATION IN FUNCTION, BY NOT THE SAME

double question mark javascript

b = a ?? -1
_____________
if(a != null){
	b = a;
}
else{
	b = -1;
}