promiseFor(), tidies up the messy nature of Promises with for-loops

promiseFor.js

//promiseFor creates 'n' promises, and returns them as a promise
// This only resolves if all the promises resolve
// It takes an integer and a Promise-like function
// The promise-like function should take 3 arguments:
  //  - An integer, representing an index
  //      or a number meaningful to your function
  //  - The standard Promise resolve function
  //  - The standard Promise reject function
function promiseFor(forCount,promiseFn){
  //return a promise
  return new Promise(function(res,rej){
    var a=[];
    for(var i=0;i<forCount;i++){
      //create all our inner promises
      a.push(new Promise(
        function(res,rej){
          promiseFn.call(null,i,res,rej);
        }
      ));
    }
    Promise.all(a).then(res,rej);
  });
}

In retrospect, I feel like this is dumb.

You're probably better off mapping an array and wrapping it in a Promise.all. It might mean building lots of new functions, rather than calling a single function, if not handled quite right, but it means you're not depending on just an index in your Promise-like function.

The intention would certainly be clearer, at least.