写一个方法获取图片的原始宽高

    function loadImageAsync(url) {        return new Promise(function(resolve, reject) { var image = new Image(); image.onload = function() {     var obj = {         w: image.naturalWidth,         h: image.naturalHeight     }     resolve(obj); }; image.onerror = function() {     reject(new Error('Could not load image at ' + url)); }; image.src = url;        });    }