More operators: Logical nullish assignment

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Remember the nullish coalescing operator ??.

We can combine it with an assignment and we get the logical nullish assignment operator ??=.

Here’s an example: you have a variable color that is set to ‘yellow’.

Using the logical nullish assignment we can say “if this variable is nullish, set it to ‘red’.”

let color = 'yellow'

color ??= 'red'

color

Try setting color to null or leaving it uninitialized; in the end color will be red.

One place where this is particularly useful is when you pass an object to a function, and this object may or may not have some properties set:

const say = (something) => {
  something.content ??= 'hello'

  console.log(something.content)
}

say({ content: 'x' })

In this case it prints ‘x’, but try passing an empty object—it will print ‘hello’.

A more verbose way to achieve something similar (using falsy check instead of nullish) would be:

const say = (something) => {
  if (!something.content) {
    something.content = 'hello'
  }

  console.log(something.content)
}