Converting data URI to image data

Question

/**
 * Converts data URI in 'image/png' format to an image data object
 * @param dataURL Base64 encoded string
 * @returns {ImageData/undefined}
 */
convertDataURLToImageData: function (dataURL) {
    if (dataURL !== undefined && dataURL !== null) {
        var canvas, context, image, imageData;
        canvas = document.createElement('canvas');
        canvas.width = 470;
        canvas.height = 470;
        context = canvas.getContext('2d');
        image = new Image();

        image.addEventListener('load', function(){
            context.drawImage(image, 0, 0, canvas.width, canvas.height);
            imageData = context.getImageData(0, 0, canvas.width, canvas.height);
            //how do i return this?
        }, false);
        image.src = dataURL;

        return imageData;
     }
}

considering the snippet above, if I would like to get an array of image data from a data URL I wold draw it on a canvas , how do I return the image data?

Answer 1

The problem is that your function is asynchronous, because you are waiting for the load event.

Then, you could use promises:

function convertURIToImageData(URI) {
  return new Promise(function(resolve, reject) {
    if (URI == null) return reject();
    var canvas = document.createElement('canvas'),
        context = canvas.getContext('2d'),
        image = new Image();
    image.addEventListener('load', function() {
      canvas.width = image.width;
      canvas.height = image.height;
      context.drawImage(image, 0, 0, canvas.width, canvas.height);
      resolve(context.getImageData(0, 0, canvas.width, canvas.height));
    }, false);
    image.src = URI;
  });
}
var URI = "data:image/x-icon;base64,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";
convertURIToImageData(URI).then(function(imageData) {
  // Here you can use imageData
  console.log(imageData);
});