CODEWITHSUNDEEP
javascriptasynchronousforeach
Tijl Declerck
Tijl Declerck

Reputation: 105

Asynchronous forEach function returns undefined

I'm trying to build an asynchronous forEach function, but unfortunately it returns the value undefined instead of the content of the array for which I had hoped for. What am I doing wrong?

function asyncforEach(array, cb) {
    array.forEach(function(){
        setTimeout(cb, 0);
    });
}

asyncforEach([1,2,3,4], function(i) {
    console.log(i)
});

Upvotes: 0

Views: 352

Answers (2)

Cerbrus
Cerbrus

Reputation: 72857

Pass the variable (value) to the callback, in setTimeout.

function asyncforEach(array, cb) {
  array.forEach(function(value){ // value: The current array entry
    setTimeout(cb, 0, value);    // Pass it to the callback when setTimeout invokes it.
  });
}
    
asyncforEach([1,2,3,4], function(i) {
  console.log(i)
});

Any parameters passed to setTimeout after the function and delay parameters, are passed to the callback:

var timeoutID = scope.setTimeout(function[, delay, param1, param2, ...]);

Upvotes: 4

Suren Srapyan
Suren Srapyan

Reputation: 68655

You missed to get the item in the forEach function parameter and pass the item into the setTimeout, Also call the cb function with passed array item into it. This will force the cb function to be called inside the arrow function, when the time will be out.

function asyncforEach(array, cb) {
    array.forEach(function(i) {
        //-----------------^---
        setTimeout( () => cb(i), 0);
        //----------^^^^^^^^^^^----
    });
}

asyncforEach([1,2,3,4], function(i) {
    console.log(i)
});

Upvotes: 2

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