使用文件阅读器获取图像的宽度和高度

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 get 0 in console.log. This requires feeding the width and the height of the original image into another script (which I'll do after, just need them in console.log/a variable for now)

function doProfilePictureChangeEdit(e) {
    var files = document.getElementById('fileupload').files[0];
    var reader = new FileReader();
    reader.onload = (function(theFile) {
        document.getElementById('imgresizepreview').src = theFile.target.result;

        document.getElementById('profilepicturepreview').src = theFile.target.result;
      }
    );
    reader.readAsDataURL(files);
    var imagepreview = document.getElementById('imgresizepreview');
    console.log(imagepreview.offsetWidth);
    $('img#imgresizepreview').imgAreaSelect({
        handles: true,
        enable: true,
        aspectRatio: "1:1",
        onSelectEnd: preview
    });
    $('#resizeprofilepicturemodal').modal('show');
    };

Answer 1

You have to wait for the image to load. Try handling the element inside .onload .

I've also simplified the process of setting the source of the two elements to how you should be doing it (with jQuery).

reader.onload = (function(theFile) { 
    var image = new Image();
    image.src = theFile.target.result;

    image.onload = function() {
        // access image size here 
        console.log(this.width);

        $('#imgresizepreview, #profilepicturepreview').attr('src', this.src);
    };
});

Answer 2

For me the solution of Austin didn't work, so I present the one worked for me:

var reader = new FileReader;

reader.onload = function() {
    var image = new Image();

    image.src = reader.result;

    image.onload = function() {
        alert(image.width);
    };

};

reader.readAsDataURL(this.files[0]);

And if you find that assignment image.src = reader.result; takes place after image.onload a bit wired, I think so too.

Answer 3

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;
}

Answer 4

 fileChangeEventHeader(fileInput) { const oFReader = new FileReader(); oFReader.readAsDataURL(fileInput.target.files[0]); oFReader.onload = (event: any) => { var image = new Image(); image.src = event.target.result; image.onload = function () { console.log(`width : ${image.width} px`, `height: ${image.height} px`); }; }; }

 <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.7.5/angular.min.js"></script> <input type="file" name="profile_img" accept="image/*" (change)="fileChangeEventHeader($event)" class="input-file">

Answer 5

this is the way I have for AngularJS

 fileReader.readAsDataUrl($scope.file, $scope).then(function(result) { var image = new Image(); image.src = result; image.onload = function() { console.log(this.width); }; $scope.imageSrc = result; //all I wanted was to find the width and height });