Convert a call using (arg1, arg2, success, error) into a Promise

Question

I'm using a third party library that exposes functions of the form function(arg1, arg2, successFunction, errorFunction).

To prevent my code from nesting success functions levels deep, I would like to use Promise.all

Is this possible? If so, how?

Possible duplicate of [How do I convert an existing callback API to promises?](https://stackoverflow.com/questions/22519784/how-do-i-convert-an-existing-callback-api-to-promises) — John, Nov 06 '17 at 14:29

alfredopacino · Accepted Answer · 2017-11-07T01:04:27.937

1

You can create a Promise wrapper to your third library:

function Promise_wrapper(arg1, arg2){
    return new Promise(function (resolve, reject){
        yourLib(arg1, arg2, function(result){
            resolve(result)
        }, function(error){
            reject(error)
        })
  });
}

obiouvsly now you can call Promise.all() with an array of Promise_wrapper

edited Nov 07 '17 at 01:04

answered Nov 06 '17 at 14:26

alfredopacino

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score 0 · Answer 2 · answered Nov 06 '17 at 14:26

You can use promise like below:

function yourMethodReturningPromise(arg1, arg2) {
  return new Promise((resolve, reject) => {
    yourFunctionUsingCallback(arg1, arg2, (something) => resolve(something), () => reject("errors")).  
  });
}

The you can use yourMethodReturningPromise like below:

yourMethodReturningPromise(arg1, arg2).then((res) => {
    console.log("success: ", res);
}, (err) => console.log("errors"))

score 0 · Answer 3 · answered Nov 07 '17 at 04:47

It's quite simple: Use the Promise constructor and just pass resolve as the successFunction callback and reject as the errorFunction callback:

var promise = new Promise((resolve, reject) => {
    libraryFunction(arg1, arg2, resolve, reject);
});

You might want to wrap this in a helper function that takes only arg1 and arg2 as parameters and returns the promise.

Convert a call using (arg1, arg2, success, error) into a Promise

3 Answers3