Q.js Q.all() when the length of array of promise is not sure

Question

I want to return an array of promise using Q.all(); like this:

return Q.all([
              list[0].getCssValue('height'),
              list[1].getCssValue('height'),
              ...,
              list[list.length-1]
              .getCssValue('height')
             ]);

I need to return all list in the array and I can get the length by array.length.

The question is that I can't

   for(var i = 0; i < list.length; i++)

to make the return items like

list[i].getCssValue('height');

So how should I do this?

Notice that `Q.all` will give a promise for an array, not an array of promises. — Bergi, Aug 28 '14 at 08:51
Do your `getCssValue` function return a promise for a single value? Can you post its code? — Bergi, Aug 28 '14 at 08:52

score 0 · Accepted Answer · answered Aug 28 '14 at 06:07

Well, you actually can do it by creating a new array:

var arr = []
for(var i = 0; i < list.length; i++){
    arr.push(list[i].getCssValue('height');
}
return Q.all(arr); // wait for all getCssValue actions

However, there is a more elegant way with .map that maps each element from an array to another:

return Q.all(arr.map(function(x){ return x.getCssValue('height'); });

Q.js Q.all() when the length of array of promise is not sure

1 Answers1