判断浏览器的javascript版本的代码

var JS_ver = [];
(Number.prototype.toFixed)?JS_ver.push("1.5"):false;
([].indexOf && [].forEach)?JS_ver.push("1.6"):false;
((function(){try {[a,b] = [0,1];return true;}catch(ex) {return false;}})())?JS_ver.push("1.7"):false;
([].reduce && [].reduceRight && JSON)?JS_ver.push("1.8"):false;
("".trimLeft)?JS_ver.push("1.8.1"):false;
JS_ver.supports = function()
{
if (arguments[0])
return (!!~this.join().indexOf(arguments[0] +",") +",");
else
return (this[this.length-1]);
}
alert("Latest Javascript version supported: "+ JS_ver.supports());
alert("Support for version 1.7 : "+ JS_ver.supports("1.7"));

<script type="text/javascript">
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';
}
}
}
}
}
}
alert(javascriptVersion);
</script>