How to return variable from anonymous function

Question

I need to return a variable from a function with anonymous functions inside of it.

Like this:

function resize(f) {

    ...

    reader.onloadend = function() {
     ...

      image.onload = function() {
       ...
        finalFile = dataURItoBlob(canvas.toDataURL(fileType));
      }
    }

}

I need to return the variable finalFile to another variable that called this function, but it keeps returning null, even if I set Global variable it doesn't work. Any idea?

Answer 1

onload and functions like it are asynchronous and need callback functions.

You cannot return from them.