How to run multiple async functions then execute callback

Question

In my NodeJS code I need to make 2 or 3 API calls, and each will return some data. After all API calls are complete I want to collect all the data into a single JSON object

Answer 1

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/all

Promise.all is now included with ES6 so you don't need any 3rd party libraries at all.

"Promise.all waits for all fulfillments (or the first rejection)"

I've setup a gist to demonstrate Promise.all() with refactoring itterations at: https://gist.github.com/rainabba/21bf3b741c6f9857d741b69ba8ad78b1

I'm using an IIFE (Immediately Invoked Function Expression). If you're not familiar, you'll want to be for the example below though the gist shows how with using an IIFE. https://en.wikipedia.org/wiki/Immediately-invoked_function_expression

TL;DR

( function( promises ){
    return new Promise( ( resolve, reject ) => {
        Promise.all( promises )
            .then( values => {
                console.log("resolved all promises")
                console.dir( values );
                resolve( values.reduce( (sum,value) => { return sum+value }) ); //Use Array.prototype.reduce() to sum the values in the array
            })
            .catch( err => {
                console.dir( err );
                throw err;
            });

    });
})([ 
    new Promise( ( resolve, reject ) => {
        console.log("resolving 1");
        resolve( 1 );
    }),
    new Promise( ( resolve, reject ) => {
        console.log("resolving 2");
        resolve( 2 );
    })
 ]).then( sum => { console.dir( { sum: sum } ) } )