Question

Given the following function:

function check_min_sizing (input, options) {
  reader = new FileReader();
  reader.onload = function (e) {
    img_rsc = e.target.result;
    image = new Image();
    image.onload = function () {
      if (image.width < options.min_width || image.height < options.min_height) {
        return false;
      } else {
        return true;
      }
    };
    image.src = img_rsc;
  };
  reader.readAsDataURL(input.files[0]);
}

How can I make the whole function return true or false? It doesn’t work as-is above because (I believe) the function finishes executing before the onload’s do…

I want to be able to do something like:

if (check_min_sizing(input, options)) {
  // do something successful
} else {
  // throw an error
}

Answer 1

There are ways of making this work, by blocking the function until the image has loaded but its a bad thing to do. The calling code should pass in a callback function, or two if you want an error callback a well.

check_min_sizing(input, options, function(e){
  // do something successful
}, function(error){
  // throw an error
});