javascript - HTML5 - how to get image dimension

Question

I have this script, it's used to fetch the width and the height of browser uploaded image.

reference: http://renevier.net/misc/resizeimg.html

function createReader(file) {
    reader.onload = function(evt) {
        var image = new Image();
        image.onload = function(evt) {
            var width = this.width;
            var height = this.height;
            alert (width); // will produce something like 198
        };
        image.src = evt.target.result; 
    };
    reader.readAsDataURL(file);
}

for (var i = 0, length = input.files.length; i < length; i++) {
    createReader(input.files[i]);
}

I want to access the value width and height from outside the createReader function. How can I do that?

Answer 1

Change "createReader" so that you pass in a handler function to be called when the image is available:

function createReader(file, whenReady) {
    reader.onload = function(evt) {
        var image = new Image();
        image.onload = function(evt) {
            var width = this.width;
            var height = this.height;
            if (whenReady) whenReady(width, height);
        };
        image.src = evt.target.result; 
    };
    reader.readAsDataURL(file);
}

Now when you call it, you can pass in a function to do whatever it is you want done with the image dimensions:

  createReader(input.files[i], function(w, h) {
    alert("Hi the width is " + w + " and the height is " + h);
  });