这些年，我收集的JavaScript代码(二)

一、JavaScript跨平台事件

　　对于跨平台事件我们一般这么写(只例举添加事件)：

function addEventHandler(oTarget, sEventType, fnHandler){    if(oTarget.addEventListener){        oTarget.addEventListener(sEventType,fnHandler,false);    } else if(oTarget.attachEvent){        oTarget.attachEvent("on"+sEventType,fnHandler);    } else{        oTarget["on"+sEventType]=fnHandler;    }}

　　那么下面这段代码的效果是什么样的呢？

<div id="test">Test</div>...var oDiv=document.getElementById("test");addEventHandler(oDiv,"mouseover",function(){    alert("over "+this.id);});

　　由于IE的this问题，在IE中果断地弹出了 over undefined，所以跨平台的事件更好的写法是这样的：

function addEventHandler(oTarget, sEventType, fnHandler){    if(oTarget.addEventListener){        oTarget.addEventListener(sEventType,fnHandler,false);    } else if(oTarget.attachEvent){        oTarget.attachEvent("on"+sEventType,function(){            return fnHandler.call(oTarget,window.event);        });    } else{        oTarget["on"+sEventType]=fnHandler;    }}

二、合并两个Array并去掉重复项

Array.prototype.unique = function() {    var a = this.concat();    for(var i=0; i<a.length; ++i) {        for(var j=i+1; j<a.length; ++j) {            if(a[i] === a[j])                a.splice(j, 1);        }    }    return a;};//Demovar array1 = ["a","b"];var array2 = ["b", "c"];var array3 = array1.concat(array2).unique();// ["a","b","c"]

三、typeof === "undefined" vs. != null

if(typeof neverDeclared == "undefined") //no errorsif(neverDeclared == null) //throws ReferenceError: neverDeclared is not defined

　　so，typeof === "undefined" is better!

四、setTimeout(fn, 0)的意义

　　浏览器同时要做很多事，这些事情以队列的方式存在，执行JavaScript只是其中之一，setTimeout(fn, 0)表面上看是立即执行的意思，但实际上只是在浏览器事件队列中添加了一个新的事件，由于队列是先进先出，所以fn会等等到当前队列中的事件执行完后再执行。由于JavaScript的定时器回调函数是异步执行的，所以产生的效果就是等页面上同步事件(包括页面渲染与同步JS代码)执行完之后再执行。

　　一个简单的示例：

<script type="text/javascript">    //one    document.getElementById("imgTest").style.borderBottom="5px solid #000";    //two    setTimeout(function(){        document.getElementById("imgTest").style.borderBottom="5px solid #000";    }, 0);</script><img src="http://jscode.chinacxy.com/img_lib/m_400_600_01.jpg" id="imgTest" alt=""/>

　　one会报错，因为页面执行到这里时还没有img，但two却可以。

五、增强版取URL中的参数

function getQueryString() {  var result = {}, queryString = location.search.substring(1),      re = /([^&=]+)=([^&]*)/g, m;  while (m = re.exec(queryString)) {    result[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);  }  return result;}// demovar myParam = getQueryString()["myParam"];

六、检查一个object是否是jQuery object

if(obj instanceof jQuery)

七、检查一个数是否为整数或浮点数

function isInt(n) {   return typeof n === 'number' && n % 1 == 0;}// or ,this support ie3function isInt(n) {   return typeof n === 'number' && parseFloat(n) == parseInt(n, 10) && !isNaN(n);}function isFloat (n) {  return n===+n && n!==(n|0);}

八、用JavaScript添加style节点

var css = 'h1 { background: red; }',    head = document.getElementsByTagName('head')[0],    style = document.createElement('style');style.type = 'text/css';if(style.styleSheet){    style.styleSheet.cssText = css;}else{    style.appendChild(document.createTextNode(css));}head.appendChild(style);

九、如何跳出双重循环

function foo (){    dance:    for(var k = 0; k < 4; k++){        for(var m = 0; m < 4; m++){            if(m == 2){                break dance;            }        }    }}

十、把一个Array追加到另一个Array上

var a=[1,2],b=[3,4,5];a.push.apply(a,b);/*a: [1, 2, 3, 4, 5]*/

十一、用jQuery把页面上的一个tag换成另一个tag

　　如把页面上所有的code换为pre：

<code> A </code><code> B </code><code> C </code>//change to<pre> A </pre><pre> A </pre><pre> A </pre>

　　jQuery代码：

$('code').contents().unwrap().wrap('<pre/>');//or$('code').replaceWith(function(){    return $("<pre />").append($(this).contents());});

十二、取数组中的最小值和最大值

var arr = new Array();arr[0] = 100;arr[1] = 0;arr[2] = 50;var min = Math.min.apply(null, arr),    max = Math.max.apply(null, arr);

十三、取两个数组交集

/* finds the intersection of  * two arrays in a simple fashion.   * * PARAMS *  a - first array, must already be sorted *  b - second array, must already be sorted * * NOTES * *  Should have O(n) operations, where n is  *    n = MIN(a.length(), b.length()) */function arrayIntersection(a, b){  var ai=0, bi=0;  var result = new Array();  while( ai < a.length && bi < b.length )  {     if      (a[ai] < b[bi] ){ ai++; }     else if (a[ai] > b[bi] ){ bi++; }     else /* they're equal */     {       result.push(a[ai]);       ai++;       bi++;     }  }  return result;}console.log(arrayIntersection([1,2,3],[2,3,4,5,6]));//[2,3]

　　注释中已经说明了，传入的数组要已经排过序的。

十四、统计一个字符串中某段子串出现的次数

var temp = "This is a string.";var count = temp.match(/is/g).length;

十五、方法返回多个值

//Onevar mValues= function(){      var a ="a";     var b = "b";       return [a, b];  };var values= mValues();var valOne= values[0];var valTwo = values[1];//Twovar mValues= function(){      var a= "a";    var b = "b";        return {        'a': a,        'b': b    };  };var values= mValues();var valOne= values.a;var valTwo = values.b;

十六、Array迭代器

function createIterator(x) {    var i = 0;     return function(){       return x[i++];    };}var iterator=createIterator(['a','b','c','d','e','f','g']);var current;while(current=iterator()){    console.log(current);}

　　注意，如果数组中有0、false、""、null、NaN迭代器将会停止。

十七、根据日计算年龄

function getAge(dateString) {    var today = new Date();    var birthDate = new Date(dateString);    var age = today.getFullYear() - birthDate.getFullYear();    var m = today.getMonth() - birthDate.getMonth();    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {        age--;    }    return age;}

console.log(getAge("2005,8,1"));//6

十八、判断当前页面是否被放入了iframe中

if(self==top){      //not in iframe}else{      //in iframe}

　　这段代码可以用来防止网页被放入iframe中，不过如果别人定义了self和top变量覆盖了浏览器默认值可能会失效。

十九、把arguments转换为Array

var args = Array.prototype.slice.call(arguments, 0);

二十、日期格式化
　　来源：javascript日期格式化函数，跟C#中的使用方法类似

Date.prototype.toString=function(format,loc){    var time={};    time.Year=this.getFullYear();    time.TYear=(""+time.Year).substr(2);    time.Month=this.getMonth()+1;    time.TMonth=time.Month<10?"0"+time.Month:time.Month;    time.Day=this.getDate();    time.TDay=time.Day<10?"0"+time.Day:time.Day;    time.Hour=this.getHours();    time.THour=time.Hour<10?"0"+time.Hour:time.Hour;    time.hour=time.Hour<13?time.Hour:time.Hour-12;    time.Thour=time.hour<10?"0"+time.hour:time.hour;    time.Minute=this.getMinutes();    time.TMinute=time.Minute<10?"0"+time.Minute:time.Minute;    time.Second=this.getSeconds();    time.TSecond=time.Second<10?"0"+time.Second:time.Second;    time.Millisecond=this.getMilliseconds();    time.Week=this.getDay();    var MMMArrEn=["Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"];    var MMMArr=["一月","二月","三月","四月","五月","六月","七月","八月","九月","十月","十一月","十二月"];    var WeekArrEn=["Sun","Mon","Tue","Web","Thu","Fri","Sat"];    var WeekArr=["星期日","星期一","星期二","星期三","星期四","星期五","星期六"];    var oNumber=time.Millisecond/1000;    if(format!=undefined && format.replace(/\s/g,"").length>0){        if(loc!=undefined && loc =="en"){            MMMArr=MMMArrEn.slice(0);            WeekArr=WeekArrEn.slice(0);        }        format=format            .replace(/yyyy/ig,time.Year)            .replace(/yyy/ig,time.Year)            .replace(/yy/ig,time.TYear)            .replace(/y/ig,time.TYear)            .replace(/MMM/g,MMMArr[time.Month-1])            .replace(/MM/g,time.TMonth)            .replace(/M/g,time.Month)            .replace(/dd/ig,time.TDay)            .replace(/d/ig,time.Day)            .replace(/HH/g,time.THour)            .replace(/H/g,time.Hour)            .replace(/hh/g,time.Thour)            .replace(/h/g,time.hour)            .replace(/mm/g,time.TMinute)            .replace(/m/g,time.Minute)            .replace(/ss/ig,time.TSecond)            .replace(/s/ig,time.Second)            .replace(/fff/ig,time.Millisecond)            .replace(/ff/ig,oNumber.toFixed(2)*100)            .replace(/f/ig,oNumber.toFixed(1)*10)            .replace(/EEE/g,WeekArr[time.Week]);    }    else{        format=time.Year+"-"+time.Month+"-"+time.Day+" "+time.Hour+":"+time.Minute+":"+time.Second;    }    return format;}var d=new Date();console.log(d.toString());    //2012-7-27 9:26:52console.log(d.toString(""));    //2012-7-27 9:26:52console.log(d.toString("yyyy-MM-dd HH:mm:ss"));    //2012-07-27 09:26:52console.log(d.toString("yyyy年MM月dd日 HH:mm:ss"));    //2012年07月27日 09:26:52console.log(d.toString("yyyy-MM-dd HH:mm:ss fff"));    //2012-07-27 09:26:52 237console.log(d.toString("yyyy年 MMM dd EEE"));    //2012年 七月 27 星期五console.log(d.toString("yyyy MMM dd EEE","en"));    //2012 Jul 27 Fri