Optional assignment

[jhpratt]

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Copying most of my original post for brevity:

My thought was to have the following:
this.foo ?= params?.foo;
which can be desugared to
if (($ref = params?.foo) !== undefined) { this.foo = $ref; }

I would strictly check for undefined, rather than nullish, as anything other than undefined would indicate that a value is present that can be set. If no value is present (such as a missing key on an object), nothing would be set. A reference must be used for the general case, as the object
being assigned (the RHS) could be a function or getter with side-effects.

Not sure if it should be ?= or =?, as it would look somewhat odd (IMO) for things like ?+= or +=?.

After looking at some prior discussion regarding ??, my original thought could be expanded to nullish, not just undefined, but that wouldn't make as much sense to me, given the difference between the two.

[jridgewell]

👋

At the March TC39 meeting the committee decided that null-coalescing assignment was a requirement for Stage 2 advancement.

Whatever syntax/semantics the ?? operator takes will be used when adding the ??= logical assignment operator.

[jhpratt]

@jridgewell Awesome! Did not know that. Let's hope that null coalescing will return undefined, not null, which would match this.

Feel free to close this if you'd like; I obviously wasn't aware of that decision.