个人总结的一些JavaScript技巧、实用函数、简洁方法、编程细节

var myVar  = "3.14159",str   = ""+ myVar,// to stringint   = ~~myVar, // to integerfloat  = 1*myVar, // to floatbool  = !!myVar, /* to boolean - any string with lengthand any number except 0 are true */array  = [myVar]; // to array

//字符型变量参与运算时，JS会自动将其转换为数值型（如果无法转化，变为NaN）    '10.567890' | 0    //结果: 10    //JS里面的所有数值型都是双精度浮点数,因此，JS在进行位运算时，会首先将这些数字运算数转换为整数，然后再执行运算    //| 是二进制或， x|0 永远等于x；^为异或，同0异1，所以 x^0 还是永远等于x；至于~是按位取反，搞了两次以后值当然是一样的    '10.567890' ^ 0        //结果: 10    - 2.23456789 | 0    //结果: -2    ~~-2.23456789    //结果: -2

    //JS本身时间的内部表示形式就是Unix时间戳，以毫秒为单位记录着当前距离1970年1月1日0点的时间单位    var d = +new Date(); //1295698416792

var arr =[].slice.call(arguments)

function test() {  var res = ['item1', 'item2']  res = res.concat(Array.prototype.slice.call(arguments)) //方法1  Array.prototype.push.apply(res, arguments)       //方法2}

(int).toString(16); // converts int to hex, eg 12 => "C"(int).toString(8); // converts int to octal, eg. 12 => "14"parseInt(string,16) // converts hex to int, eg. "FF" => 255parseInt(string,8) // converts octal to int, eg. "20" => 16

var a = [1,2,3,7,8,9];var b = [4,5,6];var insertIndex = 3;a.splice.apply(a, Array.prototype.concat(insertIndex, 0, b));

var a = [1,2,3,4,5];a.splice(3,1);      //a = [1,2,3,5]

var ie = /*@cc_on !@*/false;

// 貌似是最短的，利用IE不支持标准的ECMAscript中数组末逗号忽略的机制var ie = !-[1,];// 利用了IE的条件注释var ie = /*@cc_on!@*/false;// 还是条件注释var ie//@cc_on=1;// IE不支持垂直制表符var ie = '/v'=='v';// 原理同上var ie = !+"/v1";

var numbers = [3,342,23,22,124];var max = 0;for(var i=0;i<numbers.length;i++){ if(numbers[i] > max){  max = numbers[i]; }}alert(max);

var numbers = [3,342,23,22,124];numbers.sort(function(a,b){return b - a});alert(numbers[0]);

Math.max(12,123,3,2,433,4); // returns 433

Math.max.apply(Math, [12, 123, 3, 2, 433, 4]) //取最大值Math.min.apply(Math, [12, 123, 3, 2, 433, 4]) //取最小值

    Math.random().toString(16).substring(2);// toString() 函数的参数为基底，范围为2~36。    Math.random().toString(36).substring(2);

a=[b, b=a][0];

<h2>Great Web resources</h2><ul id="resources"> <li><a href="http://opera.com/wsc">Opera Web Standards Curriculum</a></li> <li><a href="http://sitepoint.com">Sitepoint</a></li> <li><a href="http://alistapart.com">A List Apart</a></li> <li><a href="http://yuiblog.com">YUI Blog</a></li> <li><a href="http://blameitonthevoices.com">Blame it on the voices</a></li> <li><a href="http://oddlyspecific.com">Oddly specific</a></li></ul>

// Classic event handling example(function(){ var resources = document.getElementById('resources'); var links = resources.getElementsByTagName('a'); var all = links.length; for(var i=0;i<all;i++){  // Attach a listener to each link  links[i].addEventListener('click',handler,false); }; function handler(e){  var x = e.target; // Get the link that was clicked  alert(x);  e.preventDefault(); };})();

(function(){ var resources = document.getElementById('resources'); resources.addEventListener('click',handler,false); function handler(e){  var x = e.target; // get the link tha  if(x.nodeName.toLowerCase() === 'a'){   alert('Event delegation:' + x);   e.preventDefault();  } };})();

var _IE = (function(){  var v = 3, div = document.createElement('div'), all = div.getElementsByTagName('i');  while (    div.innerHTML = '<!--[if gt IE ' + (++v) + ']><i></i><![endif]-->',    all[0]  );  return v > 4 ? v : false ;}());

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"));

// BAD: This will cause an error in code when foo is undefinedif (foo) {　　doSomething();}// GOOD: This doesn't cause any errors. However, even when// foo is set to NULL or false, the condition validates as trueif (typeof foo != "undefined") {　　doSomething();}// BETTER: This doesn't cause any errors and in addition// values NULL or false won't validate as trueif (window.foo) {　　doSomething();}

// UGLY: we have to proof existence of every// object before we can be sure property actually existsif (window.oFoo && oFoo.oBar && oFoo.oBar.baz) {　　doSomething();}

if("opera" in window){  console.log("OPERA");}else{  console.log("NOT OPERA");}

var obj=[];Object.prototype.toString.call(obj)=="[object Array]";

function doSomething() {　　// Leaves the function if nothing is passed　　if (!arguments[0]) {　　return false;　　}　　var oArgs  = arguments[0]　　arg0  = oArgs.arg0 || "",　　arg1  = oArgs.arg1 || "",　　arg2  = oArgs.arg2 || 0,　　arg3  = oArgs.arg3 || [],　　arg4  = oArgs.arg4 || false;}doSomething({　　arg1  : "foo",　　arg2  : 5,　　arg4  : false});

var sFlop  = "Flop: [Ah] [Ks] [7c]";var aValues = {"A":"Ace","K":"King",7:"Seven"};var aSuits = {"h":"Hearts","s":"Spades","d":"Diamonds","c":"Clubs"};sFlop  = sFlop.replace(//[/w+/]/gi, function(match) {　　match  = match.replace(match[2], aSuits[match[2]]);　　match  = match.replace(match[1], aValues[match[1]] +" of ");　　return match;});// string sFlop now contains:// "Flop: [Ace of Hearts] [King of Spades] [Seven of Clubs]"

outerloop:for (var iI=0;iI<5;iI++) {　　if (somethingIsTrue()) {　　// Breaks the outer loop iteration　　break outerloop;　　}　　innerloop:　　for (var iA=0;iA<5;iA++) {　　　　if (somethingElseIsTrue()) {　　　　// Breaks the inner loop iteration　　　　break innerloop;　　}　　}}

/**@desc:对数组进行去重操作，返回一个没有重复元素的新数组*/function unique(target) {  var result = [];  loop: for (var i = 0, n = target.length; i < n; i++) {    for (var x = i + 1; x < n; x++) {      if (target[x] === target[i]) {        continue loop;      }    }    result.push(target[i]);  }  return result;}

Array.prototype.distinct = function () {  var newArr = [],obj = {};  for(var i=0, len = this.length; i < len; i++){    if(!obj[typeof(this[i]) + this[i]]){      newArr.push(this[i]);      obj[typeof(this[i]) + this[i]] = 'new';    }  }  return newArr;}

Array.prototype.distinct = function () {   var sameObj = function(a, b){     var tag = true;     if(!a || !b) return false;     for(var x in a){       if(!b[x]) return false;       if(typeof(a[x]) === 'object'){         tag = sameObj(a[x],b[x]);       } else {         if(a[x]!==b[x])         return false;       }     }     return tag;   }   var newArr = [], obj = {};   for(var i = 0, len = this.length; i < len; i++){     if(!sameObj(obj[typeof(this[i]) + this[i]], this[i])){     newArr.push(this[i]);     obj[typeof(this[i]) + this[i]] = this[i];     }   }   return newArr; }

var arr=[{name:"tom",age:12},{name:"lily",age:22},{name:"lilei",age:12}];var newArr=arr.distinct(function(ele){ return ele.age;});

var i, len, maxobj='', maxnum=0, obj={};var arr = "sdjksfssscfssdd";for(i = 0, len = arr.length; i < len; i++){  obj[arr[i]] ? obj[arr[i]]++ : obj[arr[i]] = 1;  if(maxnum < obj[arr[i]]){    maxnum = obj[arr[i]];    maxobj = arr[i];  }}alert(maxobj + "在数组中出现了" + maxnum + "次");