 
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")); 

這個腳本，既能通過檢測特征來檢測JavaScript版本，還能檢查特定的Javascript版本所支持的特性。
得到了結果，我們還是看下此系統(tǒng)是如何檢測javascript版本的吧，于是將其代碼抽取出來（抽取過程相當糾結），得到如下所示代碼：

復制代碼代碼如下:

 
<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> 