How to upload an image from HTML5 canvas

The Uploader JS API allows you to upload a file from a file object. To upload an image from an HTML5 canvas,  you need to do the following:

  1. Encode a canvas to a blob object.
  2. Upload this object to Uploadcare via uploadcare.fileFrom('object', blob);

For example:

canvas.toBlob(function (blob) {
    var file = uploadcare.fileFrom('object', blob);
    file.done(function (fileInfo) {
      // file is uploaded.
    });
  }, 'image/jpeg', 0.9);

Note that canvas.toBlob is not supported by some browsers. If you’re using an unsupported browser, you might need to use a polyfill to implement this method:

if (!HTMLCanvasElement.prototype.toBlob) {
    Object.defineProperty(HTMLCanvasElement.prototype, 'toBlob', {
     value: function (callback, type, quality) {
       var binStr = atob( this.toDataURL(type, quality).split(',')[1] ),
           len = binStr.length,
           arr = new Uint8Array(len);
       for (var i=0; i<len; i++ ) {
        arr[i] = binStr.charCodeAt(i);
       }
       callback( new Blob( [arr], {type: type || 'image/png'} ) );
     }
    });
   };
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