Legitimate uses of IIFEs?

Forbes Lindesay forbes at lindesay.co.uk
Sun Dec 20 13:40:30 UTC 2015


Promises are eager.  That is, they do the work and resolve whether you await them or not.  If you want to handle exceptions, you need to call .then and provide an error handler, but other than that it's totally ok to not bother waiting for a promise.

On 19 Dec 2015, at 22:02, Mat At Bread <bread at mailed.me.uk<mailto:bread at mailed.me.uk>> wrote:


Which is what I said, I hope. Use the .then for top-level invitation. Dimitry's example wouldn't resolve the Promise

On 19 December 2015 9:24:04 pm Fabrício Matté <ultcombo at gmail.com<mailto:ultcombo at gmail.com>> wrote:

@bread I see you are referencing Dmitry's sample, but why do you say it won't work? AFAIK async functions return promises, so you don't necessarily need a top-level `await`. I believe this (extremely ugly) sample should work:

```js
function f(cb) {
  (async function() {
    // await here
  })().then(v => cb(null, v), cb);
}
```

/fm

On Sat, Dec 19, 2015 at 7:11 PM, <bread at mailed.me.uk<mailto:bread at mailed.me.uk>> wrote:
That’s not going to work. The correct form still requires an (illegal) top-level await:

await (async function() {
// await here
})();

The easiest way to spawn a top-level async function is:

here.then(function(result){},function(error){}) ;

On 19 December 2015 20:14:44 -00:00, Dmitry Soshnikov <dmitry.soshnikov at gmail.com<mailto:dmitry.soshnikov at gmail.com>> wrote:


On Saturday, December 19, 2015, Šime Vidas <sime.vidas at gmail.com<mailto:sime.vidas at gmail.com>> wrote:
With block statements + let/const, IIFEs are no longer needed to emulate block-scoped variables. That got me thinking, are there other uses of IIFEs, or are they no longer needed?
I’ve checked my code and found instances of this pattern:

var foo = (function () {
    var a, b, c; // helper variables
    // some computation
    return /* final value of foo */;
}());
Btw, there is a "do expression" proposal (stage 0) [1] for this type of pattern.
Anything else?

FWIW, one of the still valid use cases is async IIFE, to spawn an async code (since there's no yet top-level async/await)

(async function() {
  // await here
})();

Dmitry


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