Async functions inside forEach loops with js [duplicate]

Answer 1

var list = ["your", "mom"];
var count = 0;

for(var i = 0; i < list.length; ++i) {
    getSomething(list[i], function() {
     if(++count == list.length)
      imDone();
     });
}

another way is like this

var biscuits = ["cheddar", "butter milk"];

(function eatBiscuits(location) {
  eatIt(biscuits[++location], whenAllEaten);
  typeof biscuits[location] != "undefined" && eatBiscuits(location);
}(-1))

function eatIt(biscuit, cb) {
 if (typeof biscuit == "undefined") {
  cb();
 } else {
  stuffMyFace();
 }
}

Answer 2

[1,2,3,4,5,6,7,8].forEach(function(n){
 setTimeout(function(){
  console.log(arguments[0]);
 },1000*n,n);
});

This works fine for me

Answer 3

If you are willing to use a lib, then async will be a good choice (works in browsers as well as with node.js)!

async.parallel([
    function(){ ... },
    function(){ ... }
], callback);

async.series([
    function(){ ... },
    function(){ ... }
]);

Answer 4

Actually there is no 'smart' way to do it. You need to use something like setTimeout, setInterval, Worker

Answer 5

Array.prototype.forEachDone = function(fn, scope, lastfn) {
    for(var i = 0, c = 0, len = this.length; i < len; i++) {
        fn.call(scope, this[i], i, this, function() {
            ++c === len && lastfn();
        });
    }
};

[1,2,3].forEachDone(function(num, i, arr, done){
  setTimeout(function(){ console.log(num); done() }, 200);
}, this, function() {
    console.log('done counting!');
});

this will do what you're looking for. forEachDone will take the exact same parameters as forEach, with an additional one at the end that is a callback to be called when the functions applied to each element of the array are done. the function that'll be applied to each element in the array also takes the exact same parameters as in forEach but also with an additional one that is a function that should be called when the function finishes.

PS: personally, i'd never touch a native object's prototype, but if you're looking for pretty, this is it.

Answer 6

I tend to use a little utility function like this:

​function asyncCallback( iterations, onComplete ){
  var total = iterations.length || iterations, count = 0;
  return function( func ){
    func();
    if ( ++count == total ) onComplete();
  };
}

var arr = [1,2,3];

var async = asyncCallback(arr, function(){
  console.log('donezo!');
});

arr.forEach(function(num){
  setTimeout(function(){
    async(function(){
      console.log(num);
    });
  }, 200);
});

​