Javascript array.push in Promise.all returning undefined

Question

I have a promise and I'm pushing a value to Promise.all but it's returning undefined.

Here's the code:

 var arr = []; var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); arr.push(mypromise); }); Promise.all([arr]).then(values => { console.log(values); }); 

How can I fix this?

Answer 1

 var arr = []; var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); }); arr.push(mypromise); Promise.all(arr).then(values => { console.log(values); }); 

Try this.

Your Implementation for Promises is not proper, refer this https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

Also, you are making syntax mistakes like arr.push should be after

 var mypromise = new Promise((resolve, reject) => { resolve('mypromise'); }); 

and Promise.all accepts an array and what you are doing is wrapping an array with another array.

Answer 2

var arr = [];

var mypromise = new Promise((resolve, reject) => {
    resolve('mypromise');
    arr.push(mypromise);
}); 

Promise.all([arr]).then(values => {
    console.log(values);
});

I'll point out to you a mistake you made in your code...

var arr = []; // arr is currently an empty array
// when you create a variable mypromose, it is also currently undefined
var mypromise = new Promise((resolve, reject) => {
    resolve('mypromise');
    // even till now mypromise is undefined
    // what you are doing is arr.push(undefined)
    arr.push(mypromise);
}); 
// after it is completed, mypromise is now defined...

Hence, arr = [undefined]