javascript - Exit function only when return is called -

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i have input file used upload images. however, have validate size before upload. below code i've tried on.

i have parent function, calls method,validateimagesize( ):

$('input:file').change(function (e) {              if (validateimagesize(this))                 //             else                 alert("wrong size");          });

and method shown 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() returns 'undefined' parents, cause have yet executes onload functions.

the output need either true/ false. perhaps structure of codes incorrect.

how can solve this?

use callback, below:

var validation_callback = function(isvalid) {     if (isvalid) {         //     } 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]); };

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