How to iterate a for loop on a promise function callback angular

Question

I need my loop to wait for my function callback to iterate.

Here is my loop:

for(var i=0;i<tab.length;i++)
{
    this.fileService.download(tab[i]).then(success => {
        console.log("download : "+success);
    });
}
console.log("end");

for now my process just start the download and iterate, I want it to end the download function before iterate..

Thank you :)

Does this answer your question? [Asynchronous Process inside a javascript for loop](https://stackoverflow.com/questions/11488014/asynchronous-process-inside-a-javascript-for-loop) — Liam, Nov 15 '19 at 12:41

score 1 · Answer 1 · answered Nov 15 '19 at 12:47

1

You can do it like this:

Promise.all(tab.map(t => this.fileService.download(t)).then(success => {
    console.log("download : "+success);
});

But better solution here will be rxjs's Observable + async pipe

answered Nov 15 '19 at 12:47

Kasabucki Alexandr

620
3
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score 0 · Accepted Answer · answered Nov 15 '19 at 12:55

on every iteration of your for loop you're firing a promise, but you're not waiting for them to finish. You can do that using Promise.all

try

const promiseArr = tabs.map(tab => this.fileService.download(tab))
await Promise.all(promiseArr)
console.log('all files downloaded successfully')

Howeve Promise.all will only resolve if all promises in the array resolve, what if one of the promises in the array failed and you still want to do something after? For that you can use the new Promise.allSettled()

How to iterate a for loop on a promise function callback angular

2 Answers2