Getting width & height of an image with filereader

问题:

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');
    };

回答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);
    };
});

回答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.

回答3:

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


          });