canvas.toBlob polyfill

polyfill.js

if( !HTMLCanvasElement.prototype.toBlob ) {
	Object.defineProperty( HTMLCanvasElement.prototype, 'toBlob',
	{ 
		value: function( callback, type, quality )
		{
			var bin = atob( this.toDataURL( type, quality ).split(',')[1] ),
			len = bin.length,
			len32 = len >> 2,
			a8 = new Uint8Array( len ),
			a32 = new Uint32Array( a8.buffer, 0, len32 );

			for( var i=0, j=0; i < len32; i++ )
			{
				a32[i] = bin.charCodeAt(j++) |
					bin.charCodeAt(j++) << 8 |
					bin.charCodeAt(j++) << 16 |
					bin.charCodeAt(j++) << 24;
			}

			var tailLength = len & 3;

			while( tailLength-- )
			{
				a8[ j ] = bin.charCodeAt(j++);
			}

			callback( new Blob( [a8], {'type': type || 'image/png'} ) );
		}
	});
}