what does ?? mean in JS

Question

I have recently seen ?? in JS, or maybe it's a Typescript thing. It seems to behave the same as ||

code looks something like this

import GeneralImage from './images'

const Team = ({ teamImg }) => {
   return <img src={teamImg ?? GeneralImage} />
}

I would have thought to have done the following, but maybe there is a difference. Cannot find anything online for ?? but the linter doesn't seem bothered and it works the same.

const Team = ({ teamImg }) => {
   return <img src={teamImg || GeneralImage} />
}

[nullish coalescing operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator). You didn't have to delete your question... — Patrick Roberts, Feb 12 '20 at 16:56
@PatrickRoberts ah ok. When I try the demo on the man page I see the following `Error: Unexpected token '?'` — peter flanagan, Feb 12 '20 at 16:58
becuase: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator#Browser_compatibility — epascarello, Feb 12 '20 at 16:59
Don't use `??`. It has very low support - effectively a FF extension at this point as part of a proposal. — user2864740, Feb 12 '20 at 17:01
is it a new feature? Just supported for Firefox? @user2864740 — peter flanagan, Feb 12 '20 at 17:01
@peterflanagan It's not defined in any published ECMAScript standard, including ES6. Right now, *`??` is a vendor-specific non-standard language extension*. So yes, it's a "feature" of FF that should not be generally used. — user2864740, Feb 12 '20 at 17:02
and @PatrickRoberts is it just to cover cases if you consider 0, '', or NaN as valid values? — peter flanagan, Feb 12 '20 at 17:04
@user2864740 — Given this is the year of ES11, it isn't much of a surprise that ES6 doesn't have bleeding edge features :) — Quentin, Feb 12 '20 at 17:04
@user2864740 "including ES6"... that seems irrelevant. The only relevant standard in my opinion would be ES2020 — Patrick Roberts, Feb 12 '20 at 17:04
@PatrickRoberts Then tag the question appropriately and add disclaimers. Now, back in the real world, I've some coffee to refill.. — user2864740, Feb 12 '20 at 17:05
updated the tag. Tagged it with ES6 as was unsure if it was a new feature that I had missed — peter flanagan, Feb 12 '20 at 17:06
@peterflanagan — It is new. It's just a Stage 4 Proposal which will probably be in ES2020, not part of the ES6 spec from 2015. — Quentin, Feb 12 '20 at 17:09
thanks @Quentin The tag has been removed so everyone can rest easy tonight — peter flanagan, Feb 12 '20 at 17:09
@PatrickRoberts once introduced can you see it been used more often than the more traditional `||` — peter flanagan, Feb 12 '20 at 17:12
@peterflanagan We have null coalesce in PHP and I use it as a switch. Especially if an argument is typed, for instance (`?string $name`), you can do a switch-thru (like fall-through, like Maybe or Optionals) to respond to a non-property: `$fullname = $name ?? $user['name'];` It is not the same, at least in PHP, as a falsey optional, which is `?:` and called a short ternary. — Jared Farrish, Feb 12 '20 at 17:16
@Quentin not "probably", [it already is](https://tc39.es/ecma262/#prod-CoalesceExpression) — Patrick Roberts, Feb 12 '20 at 17:51
@PatrickRoberts do you predict it to be used over `||` once released? — peter flanagan, Feb 12 '20 at 18:20
@peterflanagan asking for opinions is [off-topic](https://stackoverflow.com/help/on-topic). — Patrick Roberts, Feb 12 '20 at 19:24
@PatrickRoberts whoops, sorry for breaking the rules where is the best place I can ask you for your opinion? Do you have an email address, or maybe a telephone number I could contact you on? — peter flanagan, Feb 12 '20 at 22:21

what does ?? mean in JS

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