CODEWITHSUNDEEP
javascriptconditional-operatorassignment-operatornullish-coalescing
Proxycon
Proxycon

Reputation: 113

Is there a reverse logical nullish assignment?

So the nullish coalescing assignment operator ??= assigns the value to the variable only if the current stored value is nullish.

Maybe I'm missing the obvious but I can't think of a slick solution (without if statements) to only assign if the right-hand side value being assigned is not nullish?

I'm using nodeJS to give a bit more context.

I want

let x r??= 2;
// Updates 'x' to hold this new value
x r??= undefined;
// Has no effect, since the value to assign is nullish
console.log(x); // 2

EDIT to give more clarity to my problem:

I want a variable only to be assigned a new value, if that new value is not nullish.

let iceCream = {
    flavor: 'chocolate'
}

const foo = 2.5
const bar = undefined;

iceCream.price r??= bar
// does not assign the new value because it is nullish
console.log(iceCream.price) // expected to be error, no such property

iceCream.price r??= foo
// assigns the new value because it is not nullish but a float
console.log(iceCream.price) // expected to be 2.5

iceCream.price r??= bar
// does not assign the new value because it is nullish
console.log(iceCream.price) // expected to still be 2.5

Upvotes: 7

Views: 1819

Answers (3)

Daniel Baldi
Daniel Baldi

Reputation: 920

Adding another answer after clarification as editing my previous one seemed weird.

The simplest way I can think of a solution without if is as follows:

let iceCream = {
    flavor: 'chocolate'
}

const foo = 2.5
const bar = undefined;
bar && (iceCream.price = bar)
// Another possible solution if creating the property with a nullish value is ok for you:
iceCream.price = bar || iceCream.price;

Upvotes: 0

Daniel Baldi
Daniel Baldi

Reputation: 920

You could use logical AND assignment.

From the MDN Web Docs:

let a = 1;
let b = 0;

a &&= 2;
console.log(a);
// expected output: 2

b &&= 2;
console.log(b);
// expected output: 0

Upvotes: -2

Ry-
Ry-

Reputation: 225164

No, that’s not a single operator. The closest is two operators:

x = undefined ?? x;

Upvotes: 6

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