Typescript

Question

Why this code produce errors?

let promises = [p1(), p2(), p3()];
$q.all(promises)
  .then(([p1Result, p2Result, p3Result]) => {
    // ...
  });

But when I turn it to this, it works:

let promises = [p1(), p2(), p3()];
$q.all(promises)
  .then(results => {
    let [p1Result, p2Result, p3Result] = results;
    // ...
  });

Another problem I have is that I can't define a type for p1Result, p2Result, p3Result. Not to mention that Typescript compiler does not infer types of them.

Ideally both should just work fine. And you can define the type as [p1Result, p2Result, p3Result]:[p1Type, p2Type, p3Type] or even results:[p1Type, p2Type, p3Type]. What is the error you see? — PSL
– PSL, Commented Oct 27, 2015 at 14:46

basarat · Accepted Answer · 2015-10-27 23:38:00Z

1

They both work the same

declare var $q: any;
declare var p1: any;
declare var p2: any;
declare var p3: any;
let promises = [p1(), p2(), p3()];


$q.all(promises)
  .then(([p1Result, p2Result, p3Result]) => {
    // ...
  });

$q.all(promises)
  .then(results => {
    let [p1Result, p2Result, p3Result] = results;
    // ...
  });

Generated JavaScript:

var promises = [p1(), p2(), p3()];
$q.all(promises)
    .then(function (_a) {
    var p1Result = _a[0], p2Result = _a[1], p3Result = _a[2];
    // ...
});
$q.all(promises)
    .then(function (results) {
    var p1Result = results[0], p2Result = results[1], p3Result = results[2];
    // ...
});

You can see that TypeScript is happy with both code samples

answered Oct 27, 2015 at 23:38

basarat

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3 Comments

alisabzevari Over a year ago

Thanks, I think it is a bug in VS 2015. Your code gets intellisense error in VS but compiles successfully. I was relying on intellisense.

alisabzevari Over a year ago

I am using it and it gives me the best experience working with typescript, but because of other parts of code in that project we were using VS. Actually I was thinking about this today ;)

alisabzevari Over a year ago

Actually, It was Resharper's bug!

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