JS 获取图片宽高

function createReader(file, whenReady) {
    var reader = new FileReader;
    reader.onload = function(e) {
        var image = new Image();
        image.onload = function() {
            var width = this.width;
            var height = this.height;
                
            if (whenReady) whenReady(width, height);
        };
        image.src = e.target.result;
    };
    reader.readAsDataURL(file);
}