Javascript获取远程图片宽高

function getMeta(varA, varB) {
    if (typeof varB !== 'undefined') {
        alert(varA + ' width ' + varB + ' height');
    } else {
        var img = new Image();
        img.src = varA;
        img.onload = function() {
            getMeta(this.width, this.height);
        }
    }
}

getMeta("http://snook.ca/files/mootools_83_snookca.png");