is used destructuring in Promise.resolve with value thenable Object?

Question

The following code use Destructuring:

var obj = {
  fun1:function() { console.log('Working') }
};

obj = { fun1:function(){ console.log("Replaced Working")} }

obj.fun1();

//output:
//Replaced Working

Does the following Promise do the same?

var pr = Promise.resolve({then:function(resolve){
  resolve(20);
  }
})


pr.then(function(v){
  console.log(v);
})

that's mean,pr is equal Promise object that,its then method changed to:

function(resolve){
  resolve(20);
}

and finally,pr.then(function(v){...} produces result.if don't use of Destructuring ,so why there is passed then property in Promise.resolve?

Could you change your question title? It really isn't clear what it means. I don't understand "Has been used destructuring". — zero298, Jul 30 '18 at 16:10
You're just passing a thenable object literal to `Promise.resolve()` this is a documented use case. It's difficult to know what you are asking. — Mark, Jul 30 '18 at 16:15
No, it does not do the same obviously: your first snippet logs `Replaced Working`, while your second snippet (asynchronously) logs `20`. — Bergi, Jul 30 '18 at 16:21

score 2 · Accepted Answer · edited Jul 30 '18 at 16:26

2

The following code use Destructuring

No it does not. Destructuring would be

 const { fun1 } = obj;
 fun1();

You are just rewriting a property.

Does the following Promise do the same?

No it does not. resolve is an internal function of the promise constructor that then calls all the functions passed into thens. There is no property rewritten at all.

why there is passed then property in Promise.resolve?

I don't know, that makes no sense at all. If you do:

 const pr = Promise.resolve(42);
 pr.then(console.log) // 42

If you pass an object in, it will resolve to that object:

 const pr = Promise.resolve({ some: "thing" });
 pr.then(console.log); // { some: thing }

If that object has a then method it is called a thenable object and the promise will follow that function assuming is has a signature of function(onFulfill, onReject). This is what your last example it doing.

edited Jul 30 '18 at 16:26

Mark

90,562
7
108
148

answered Jul 30 '18 at 16:15

Jonas Wilms

132,000
20
149
151

Why not wait for clarification on the question or simply vote to close? – zero298 Jul 30 '18 at 16:16
@zero298 to prevent others from answering. And i voted to close already. – Jonas Wilms Jul 30 '18 at 16:18
This doesn't prevent anyone from answering. Voting to close prevents people from answering. – zero298 Jul 30 '18 at 16:18
@zero298 not really. It takes way to long until 5 votes are casted. And I'm also trying to help the OP which is way easier in an answer with formatting etc. – Jonas Wilms Jul 30 '18 at 16:19
@JonasW. if it has a `then`property that points to a function it *does* matter. – Mark Jul 30 '18 at 16:20
@mark right, feel free to edit / answer or should I? – Jonas Wilms Jul 30 '18 at 16:23
@JonasW. ,Thank you!!! – Ehsan Jul 30 '18 at 16:26
@nehsan no worries, this was a community achievement :) – Jonas Wilms Jul 30 '18 at 16:31

is used destructuring in Promise.resolve with value thenable Object?

1 Answers1