Promises in the foreach loop (Typescript 2)

Question

I've stuck with the promise chains, i need to proceed some code after uploading images to the server. It's Angular2 and Typescript. Lets write some pseudo-code:

uploadImages(images):Promise<any> {
    return new Promise((resolve, reject) => {
        for (let image of images) {
            upload(image.type_1).on('upload_completed', (data) => {
                 // do something
            })

            upload(image.type_2).on('upload_completed', (data) => {
                 // do something
            })
    }
}

uploadImages(images).then(doSomethingElse);

I did this task in some way like this, but i'm a bit confused with promise chains, i can't figure out how to chain this image uploads in the foreach loop and return the result it in the new promise when all uploads will be done. What is the correct way to do this?

EDIT: There are event-based callbacks in the loop, how to convert to promises them for using Promise.all()?

Solution

uploadImages(images):Promise<any> {
    let promises_array:Array<any> = [];
    for (let image of images) {
        promises_array.push(new Promise(function(resolve,reject) {
            upload(image.type_1).on('upload_completed', (data) => {
                    resolve(true);
            })
        }));
        promises_array.push(new Promise(function(resolve,reject) {
            upload(image.type_2).on('upload_completed', (data) => {
                    resolve(true);
            })
        }));
    return Promise.all(promises_array);
}
uploadImages(images).then(doSomethingElse);

Comments

[Heretic Monkey]

Promise.all()

[dr1v3]

@MikeMcCaughan, there are event-based callbacks in the loop

[Heretic Monkey]

So, they're not promises?

[JB Nizet]

Create one promise per upload (by resolving the promise in the callback), and then use Promise.all() to create a global promise out of all the individual promises.

[dr1v3]

@JBNizet i did it like above and got "TypeError: Cannot read property 'length' of undefined" error

[Heretic Monkey]

You have to initialize the array. That probably will won't work, since promises_array won't have anything in it when it gets to all... Might want to look at stackoverflow.com/q/22519784/215552

[dr1v3]

@MikeMcCaughan, yep, sorry, i made a mistake in the first code version

[dr1v3]

@MikeMcCaughan Thanks a lot!

[dr1v3]

@JBNizet Thanks a lot!

[Heretic Monkey]

@dr1v3 Feel free to post that solution as an answer. We don't like answers in the questions here, and we encourage people to answer their own questions when they've figured out themselves.