Question

I’m calling an async function that needs a callback function as parameters.

Here is the javascript code:

for(i in array) 
{
    var item = array[i];
    functionToCall(item[i][1], 50, function(a, b)
    {
        alert(a + b);
    });
}

I cannot edit functionToCall function. What I want to do is using the “item” variable in the callback function like this.

for(i in array) 
{
    var item = array[i];
    functionToCall(item[i][1], 50, function(a, b, c)
    {
        alert(a + b + c);
    }, item);
}

But this code doesn’t work properly. I cannot just use “item” inside the function because it is always using the last item in array.

So how can I do that?

Answer 1

You can use item inside the function, but you need to “capture” it so that you don’t end up using the last element of the array everytime.

for(var i = 0, l = array.length; i < l; ++i) { // better than for .. in
    var item = array[i];
    (function(item, i){
      functionToCall(item[i][1], 50, function(a, b) // do you really re-index item with the same index?
      {
          alert(a + b);
      });
    })(item, i);
}