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那些年，收集的javascript代码（二）

Posted by sqq5682 on July 15, 2017

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;
};

//Demo
var 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 errors

if(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 = /([^&amp;=]+)=([^&amp;]*)/g, m;

  while (m = re.exec(queryString)) {
    result[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);
  }

  return result;
}
// demo
var 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' &amp;&amp; n % 1 == 0;
}

// or ,this support ie3
function isInt(n) {
   return typeof n === 'number' &amp;&amp; parseFloat(n) == parseInt(n, 10) &amp;&amp; !isNaN(n);
}

function isFloat (n) {
  return n===+n &amp;&amp; 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codr换为pre：

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

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 &amp;&amp; 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

//One
var mValues= function(){  
    var a ="a"; 
    var b = "b";   
    return [a, b];  
};
var values= mValues();
var valOne= values[0];
var valTwo = values[1];
//Two
var 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 &amp;&amp; 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 &amp;&amp; format.replace(/\s/g,"").length>0){
        if(loc!=undefined &amp;&amp; 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 9:26:52
console.log(d.toString(""));    //2012-7-27 9:26:52
console.log(d.toString("yyyy-MM-dd HH:mm:ss"));    //2012-07-27 09:26:52
console.log(d.toString("yyyy年MM月dd日 HH:mm:ss"));    //2012年07月27日 09:26:52
console.log(d.toString("yyyy-MM-dd HH:mm:ss fff"));    //2012-07-27 09:26:52 237
console.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

二十一、JavaScript正则中test小用法

var str="a12b123c1234e12345";
var reg=/a(\d{2})b(\d{3})c(\d{4})/;
reg.test(str);
console.log(RegExp.$1,RegExp.$2,RegExp.$3,RegExp.$4);
// output:12 123 1234

二十二、JavaScript判断浏览器类型及主版本

function getBrowserInfo(){
    var Sys = {};
    var ua = navigator.userAgent.toLowerCase();
    if (window.ActiveXObject){
        Sys.b="ie";
        Sys.v =parseInt(ua.match(/msie ([\d.]+)/)[1]);
    }
    else if (document.getBoxObjectFor){
        Sys.b="firefox";
        Sys.v =parseInt(ua.match(/firefox\/([\d.]+)/)[1]);
    }
    else if (window.MessageEvent &amp;&amp; !document.getBoxObjectFor){
        Sys.b="chrome";
        Sys.v == parseInt(ua.match(/chrome\/([\d.]+)/)[1]);
    }
    else if (window.opera){
        Sys.b="opera";
        Sys.v == parseInt(ua.match(/opera.([\d.]+)/)[1]);
    }
    else if (window.openDatabase){
        Sys.b="safari";
        Sys.v == parseInt(ua.match(/version\/([\d.]+)/)[1]);
    }
    return Sys;
}
var bi=getBrowserInfo();
document.write("Browser:"+bi.b+"    Version:"+bi.v);//Browser:ie Version:10

转自http://www.cnblogs.com/jscode/archive/2012/07/27/2610613.html