window.showmodaldialog undefined is not a function

谷歌浏览器升级到 新版本后，window.showModalDialog这个窗口方法报错Uncaught TypeError: undefined is not a function 

我把下面的js代码放到页面的header里，是可以解决问题的。它做了以下事情：当检测到浏览器不支持showModalDialog时，使用window.open重写了这个方法。在这个方法里将dialog的参数（height, width, scroll..）做了解析,将打开的窗体居中，并设置上焦点。此外为了防止打开多个重复窗体，这里拿url作为window的名字。

if (!window.showModalDialog) {
     window.showModalDialog = function (arg1, arg2, arg3) {

        var w;
        var h;
        var resizable = "no";
        var scroll = "no";
        var status = "no";

        // get the modal specs
        var mdattrs = arg3.split(";");
        for (i = 0; i < mdattrs.length; i++) {
           var mdattr = mdattrs[i].split(":");

           var n = mdattr[0];
           var v = mdattr[1];
           if (n) { n = n.trim().toLowerCase(); }
           if (v) { v = v.trim().toLowerCase(); }

           if (n == "dialogheight") {
              h = v.replace("px", "");
           } else if (n == "dialogwidth") {
              w = v.replace("px", "");
           } else if (n == "resizable") {
              resizable = v;
           } else if (n == "scroll") {
              scroll = v;
           } else if (n == "status") {
              status = v;
           }
        }

        var left = window.screenX + (window.outerWidth / 2) - (w / 2);
        var top = window.screenY + (window.outerHeight / 2) - (h / 2);
        var targetWin = window.open(arg1, arg1, 'toolbar=no, location=no, directories=no, status=' + status + ', menubar=no, scrollbars=' + scroll + ', resizable=' + resizable + ', copyhistory=no, width=' + w + ', height=' + h + ', top=' + top + ', left=' + left);
        targetWin.focus();
     };
  }