网上招了一个js下载的代码：

/**
 * Javascript 多文件下载
 * @author Barret Lee
 * @email  barret.china@gmail.com
 */
var downHelper = (function(files){
    var h5Down = !/Trident|MSIE/.test(navigator.userAgent);
    /**
     * 在支持 download 属性的情况下使用该方法进行单个文件下载
     * 目前 FF 还不支持 download 属性，所以 FF 必须另觅他法！
     * @param  {String} fileName
     * @param  {String|FileObject} contentOrPath
     * @return {Null}
     */
    function downloadFile(fileName, contentOrPath){
        var aLink = document.createElement("a"),
            evt = document.createEvent("HTMLEvents"),
            isData = contentOrPath.slice(0, 5) === "data:",
            isPath = contentOrPath.lastIndexOf(".") > -1;

        // 初始化点击事件
        // 注：initEvent 不加后两个参数在FF下会报错
        evt.initEvent("click",false,false);

        // 添加文件下载名
        aLink.download = fileName;

        // 如果是 path 或者 dataURL 直接赋值
        // 如果是 file 或者其他内容，使用 Blob 转换
        aLink.href = isPath || isData ? contentOrPath
            : URL.createObjectURL(new Blob([contentOrPath]));

        aLink.dispatchEvent(evt);
    }

    /**
     * [IEdownloadFile description]
     * @param  {String} fileName
     * @param  {String|FileObject} contentOrPath
     */
    function IEdownloadFile(fileName, contentOrPath, bool){
        window.open(contentOrPath);
    }

    /**
     * [parseURL description]
     * @param  {String} str [description]
     * @return {String}     [description]
     */
    function parseURL(str){
        return str.lastIndexOf("/") > -1 ? str.slice(str.lastIndexOf("/") + 1) : str;
    }

    return function(files){
        // 选择下载函数
        var downer = h5Down ? downloadFile : IEdownloadFile;

        // 判断类型，处理下载文件名
        if(files instanceof Array) {
            for(var i = 0, l = files.length; i < l ; i++)
                // bug 处理
                downer(parseURL(files[i]), files[i], true);
        } else if(typeof files === "string") {
            downer(parseURL(files), files);
        } else {
            // 对象
            for(var file in files) downer(file, files[file]);
        }
    }
})();

但是调用的时候，chrome给出了警告，A DOM event generated from JavaScript has triggered a default action inside the browser. This behavior is non-standard and will be removed in M53, around September 2016. See https://www.chromestatus.com/features/5718803933560832 for more details.,我看了一下警告链接给出的说明：

According to the UI Events specification un-trusted events (i.e. those created by JavaScript) should not invoke the default action. 'click' is the only event that is a legacy permitted case.

The isTrusted support was added in https://www.chromestatus.com/... which identifies trusted events from un-trusted events.

We wish to prevent synthetic events from executing the default action, aligning with Firefox and IE.

上面代码中自定义事件，就是click类型啊，应该是一个合法的事件啊，浏览器会什么会警告呢？百思不得其解。