Exit function only when return is called

Question

i have a input file which is used to upload images. However, I have to validate its size before upload. As below is the code I've tried on.

I have a parent function, that calls the method,ValidateImageSize( ):

$('input:file').change(function (e) {

            if (ValidateImageSize(this))
                // do something
            else
                alert("wrong size");

        });

and the method shown as below:

    var ValidateImageSize = function (input) {

       var reader = new FileReader();
       reader.onload = function (e) {

           var img = new Image();
           img.onload = function (e) {
              return this.height == 40 && this.width == 40 ? true : false;
           }
           img.src = e.target.result;
       }
       reader.readAsDataURL(input.files[0]);
   };

The method ValidateImageSize() always returns 'undefined' to its parents, cause it have yet executes the onload functions.

The output I need is either true/ false. Perhaps the structure of my codes itself is incorrect.

How can I solve this?

Manoj Yadav · Accepted Answer · 2014-05-30 08:43:52Z

3

Use callback, something like as below:

var validation_callback = function(isValid) {
    if (isValid) {
        // do something
    } else {
        alert("wrong size");
    }
};

$('input:file').change(function(e) {
    ValidateImageSize(this, validation_callback);
});

var ValidateImageSize = function (input, callback) {
    var reader = new FileReader();
    reader.onload = function (e) {
        var img = new Image();
        img.onload = function (e) {
           var isValid = this.height == 40 && this.width == 40 ? true : false;
           callback(isValid);
        };
        img.src = e.target.result;
    };
    reader.readAsDataURL(input.files[0]);
};

edited May 30, 2014 at 8:43

answered May 30, 2014 at 8:02

Manoj Yadav

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