获得 Javascript 版本

<script type="text/javascript">
                function getjsversion(){
                        var n = navigator;
                        var u = n.userAgent;
                        var apn = n.appName;
                        var v = n.appVersion;
                        var ie = v.indexOf('MSIE ')
                        if(ie > 0){
                           apv = parseInt(i = v.substring(ie + 5));
                           if(apv > 3) {
                               apv = parseFloat(i);
                           }
                        }else{
                           apv = parseFloat(v);
                        }
                        var isie = (apn == 'Microsoft Internet Explorer');
                        var ismac = (u.indexOf('Mac') >= 0);
                        var javascriptVersion = "1.0";
                        if(String && String.prototype){
                           javascriptVersion = '1.1';
                           if(javascriptVersion.match){
                               javascriptVersion = '1.2';
                               var tm = new Date;
                               if(tm.setUTCDate){
                                   javascriptVersion = '1.3';
                                   if(isie && ismac && apv >= 5) javascriptVersion = '1.4';
                                   var pn = 0;
                                   if(pn.toPrecision){
                                       javascriptVersion = '1.5';
                                       a = new Array;
                                       if(a.forEach){
                                           javascriptVersion = '1.6';
                                           i = 0;
                                           o = new Object;
                                           tcf = new Function('o','var e,i=0;try{i=new Iterator(o)}catch(e){}return i');
                                           i = tcf(o);
                                           if(i && i.next) {
                                               javascriptVersion = '1.7';
                                           }
                                       }
                                   }
                               }
                           }
                        }
                        return javascriptVersion;
                }
        alert(getjsversion());
</script>