Resize Image using Javascript

by Naveen Jose

HTML

<input id="imageFile" type="file"><input type="button" value="Resize Image"  onclick="ResizeImage()"/> 
<img src="" id="output">

JavaScript

function ResizeImage() {
    var filesToUpload = document.getElementById('imageFile').files;
    var file = filesToUpload[0];

    // Create an image
    var img = document.createElement("img");
    // Create a file reader
    var reader = new FileReader();
    // Set the image once loaded into file reader
    reader.onload = function(e) {
            img.src = e.target.result;

            var canvas = document.createElement("canvas");
            //var canvas = $("<canvas>", {"id":"testing"})[0];
            var ctx = canvas.getContext("2d");
            ctx.drawImage(img, 0, 0);

            var MAX_WIDTH = 400;
            var MAX_HEIGHT = 400;
            var width = img.width;
            var height = img.height;

            if (width > height) {
                if (width > MAX_WIDTH) {
                    height *= MAX_WIDTH / width;
                    width = MAX_WIDTH;
                }
            } else {
                if (height > MAX_HEIGHT) {
                    width *= MAX_HEIGHT / height;
                    height = MAX_HEIGHT;
                }
            }
            canvas.width = width;
            canvas.height = height;
            var ctx = canvas.getContext("2d");
            ctx.drawImage(img, 0, 0, width, height);

            var dataurl = canvas.toDataURL("image/png");
            document.getElementById('output').src = dataurl;
        }
        // Load files into file reader
    reader.readAsDataURL(file);
}