Getting width & height of an image with filereader

Question

I am building an image resize/crop, and I\'d like to show a live preview after they\'ve edited it in a modal (bootstrap). This should work, I believe, but I just ge

Answer 1

Here's an answer inspired by Austin Brunkhorst with a callback for ascertaining image size in case you want to reuse the function elsewhere in your code.

fileControl is assumed to be a jQuery element.

function didUploadImage(fileControl) {      
   // Render image if file exists.
   var domFileControl = fileControl[0];
   if (domFileControl.files && domFileControl.files[0]) {
      // Get first file.
      var firstFile = domFileControl.files[0];

      // Create reader.
      var reader = new FileReader();

      // Notify parent when image read.
      reader.onload = function(e) {
         // Get image URL.
         var imageURL = reader.result;

        // Get image size for image.
        getImageSize(imageURL, function(imageWidth, imageHeight) {
            // Do stuff here.
        });
      };

      // Read image from hard disk.
      reader.readAsDataURL(firstFile);

      // Print status.
      console.log("Uploaded image: " + firstFile.name);
   }
}


function getImageSize(imageURL, callback) {      
   // Create image object to ascertain dimensions.
   var image = new Image();

   // Get image data when loaded.
   image.onload = function() {      
      // No callback? Show error.
      if (!callback) {
         console.log("Error getting image size: no callback. Image URL: " + imageURL);

      // Yes, invoke callback with image size.
      } else {
         callback(this.naturalWidth, this.naturalHeight);
      }
   }

   // Load image.
   image.src = imageURL;
}