转载

javascript编程笔记

1. 快速排序算法

方法一

function quicksort(n,left,right){   var p;   if(left<right){     p = position(n,left,right);     quicksort(n,left,p-1);     quicksort(n,p+1,right);   } }  function position(n,left,right){   var temp = n[left];   while(left<right){     while(left<right&&n[right]>temp)       right--;     if(left<right)       n[left++]=n[right];     while(left<right&&n[left]<temp)       left++;     if(left<right)       n[right--]=n[left];   }   n[left]=temp;   return left; }  var a =[50, 32, 11, 16, 32, 24, 99, 57, 100]; quicksort(a,0,a.length-1) console.log(a);

方法二

function quickSort(arr,left,right){   var p;   if(left<right){     p=position(arr,left,right);     quicksort(arr,left,p-1);     quicksort(arr,p+1,right);   }   function position(arr,left,right){     var temp=arr[left];     while(left<right){       while(left<right&&arr[right]>temp) right--;       if(left<right) arr[left++]=arr[right];       while(left<right&&arr[left]<temp) left++;       if(left<right) arr[right--]=arr[left];     }     arr[left] =temp;     return left;   } }

2. 深度克隆clone(继承)

var cloneObj = function(obj){  var str, newobj = obj.constructor === Array ? [] : {};  if(typeof obj !== 'object'){   return;  } else if(window.JSON){   str = JSON.stringify(obj), //系列化对象   newobj = JSON.parse(str); //还原  } else {   for(var i in obj){    newobj[i] = typeof obj[i] === 'object' ?     cloneObj(obj[i]) : obj[i];    }  }  return newobj; }; //测试 var obj = {a: 0, b: 1, c: 2}; var arr = [0, 1, 2]; //执行深度克隆 var newobj = cloneObj(obj); var newarr = cloneObj(arr); //对克隆后的新对象进行成员删除 delete newobj.a; newarr.splice(0,1); console.log(obj, arr, newobj, newarr); 结果： {a: 0, b: 1, c: 2}, [0, 1, 2], {b: 1, c: 2}, [1, 2]; */

3. 找出字符串或者数组中出现相同字符，并且打印出次数最多的次数和字符

var str = "abcdefgaddda";   var obj = {};   for (var i = 0, l = str.length; i < l; i++) {     var key = str[i];     if (!obj[key]) {       obj[key] = 1;     } else {       obj[key]++;     }   }    var max = -1;   var max_key = "";   var key;   for (key in obj) {     if (max < obj[key]) {       max = obj[key];       max_key = key;     }   }   alert("max:" + max + " max_key:" + max_key);

4. 解析url为json数据格式

function getUrl(url){   //var arr=url.split('?')[1].split('&');    var arr = [];   var a3= [];   arr = url.split("?");   a1 = arr[1];   a2 = a1.split("&");   obj = {};   for(var i=0;i<a2.length;i++){     a3[i] = a2[i].split("=");     obj[a3[i][0]] = a3[i][1];   } return obj;  } var url= "URL:http://item.taobao.com/item.htm?a=1&b=2&c=&d=xxx&e"; //console.log(getUrl(url));    var getjson = function(url) {   var a = [];   var obj = {};   var a = url.split('?')[1].split('&');   for (var i = 0; i < a.length; i++) {     var b[i] = a[i].split('=');     obj[b[i][0]] = b[i][1];   }   return obj; }  getjson(url);

5. 通用事件注册函数

var obj = document.getElementById("p"); var type = click； function fun() {}  function addEvent(obj, type, fun) {   if (obj.addEventListener) {     obj.addEventListener(type, fun, false);   } else if (obj.attachEvent) {     obj.attachEvent("on" + type, fun);   } else {     obj["on" + type] = fun;   } }

6. 写一个获取url中参数的值的函数

function getRequest() {   var url = window.location.search;   var oRequest = new Object();   if (url.indexOf('?') !== -1) {     url = url.substr(1); // 取得?以后的字符串     var reqArr = url.split('&');     for (var i = 0; i < reqArr.length; i++) {       oRequest[(reqArr[i].split('='))[0]] = unescape((reqArr[i].split('='))[1]);     }   }   return oRequest; }

7. JS中的数据类型？如何断定一个变量是否是String类型

var str = new String("abcd"); console.log(typeof str); // object console.log(str instanceof String); console.log(str.constructor == String); console.log(Object.prototype.toString.call(str) === "[object String]"); // true  var str1 = "abcd";  console.log(typeof str1); // string console.log(Object.prototype.toString.call(str1) === "[object String]"); // true*/

8. 请实现，鼠标点击页面中的任意标签， alert该标签的名称．（注意兼容性）

document.onclick = function(e) {   var e = e || window.event;   var obj = e.target || e.srcElement;   alert(obj.tagName.toLowerCase()); }

9. js异步加载的三种解决方案

(1) defer，只支持IE  <script type="text/javascript" defer="defer">  alert(document.getElementById("p1").firstChild.nodeValue);  </script>  (2) async： <script type="text/javascript" src="demo_async.js" async="async"></script>  (3) 创建script，插入到DOM中，加载完毕后callBack，见代码： function loadScript(url, callback){  var script = document.createElement("script");  script.type = "text/javascript";  if(script.readyState){//IE   script.onreadystatechange = function(){    if(script.readyState == "loaded" ||     script.readyState == "complete"){     script.onreadystatechange = null;     callback();    }   };  }else{//firefox,safari,chrome,opera   script.onload = function(){    callback();   };  }  script.src = url;  document.body.appendChild(script); }

10. 二分搜索，从数组中找到findvalue

function binarySearch(arr,start,end,findvalue){   var arr = arr.sort(function(a,b){return a-b});   var mid=Math.floor((start+end)/2);   var midvalue = arr[mid];   if(midvalue==findvalue){     return mid;   }else if(findvalue<midvalue){     binarySearch(arr,start,mid-1,findvalue);   }else if(findvalue>midvalue){     binarySearch(arr,mid+1,end,findvalue);   }else{     return -1;   }  }

11. javascript保留两位小数

num.toFixed(2);  function toDecimal(x) {       var f = parseFloat(x)   if(isNaN(f)){     return false;   }   var f = Math.round(x*100)/100;   var s = f.toString();   var rs = s.indexOf('.');   if(rs<0){     rs=s.length;     s+='.';   }   while(s.length<=rs+2){     s+='0';   }   return s;           }

12. 编写一个方法求一个字符串的字节长度;英文占一个，中文占两个

方法一： function getStrlen(str) {   var len = str.length;   var re = /[/u4e00-/u9fa5]/;   for(var i=0;i<str.length;i++){     if(re.test(str.charAt(i)))       len++;   }   return len; } 方法二： function getStrlen(str){   var len= str.length;   for(var i=0;i<str.length;i++){     if(str.charCodeAt(i)>255)       len++;   }   return len; }

13. 编写一个方法去掉一个数组的重复元素

function delRepeat(arr){   var a = [];   for(var i=0,l=arr.length;i<l;i++){     if(arr.indexOf(arr[i])==i){       a.push(arr[i])     }   }   return a; }

14. JavaScript中如何检测一个变量是一个String类型？请写出函数实现

typeof(obj) == 'string'; obj.constructor == String; obj instanceof String;

15. 鼠标点击页面中的任意标签， alert该标签的名称．（注意兼容性）

方法一： DOM0级事件 document.onclick = function(e){   var e = e||window.event;   var target = e.target || e.srcElement;   console.log(target.tagName.toLowerCase()); } 方法二： DOM2级事件 事件代理 function callback(e) {   var e = e || window.event;   var target = e.target || e.srcElement;   console.log(target.tagName); }  if (document.addEventListener) {   document.addEventListener('click', callback, false) } else if (document.attachEvent) {   document.attachEvent('onclick', callback) } else {   document['onclick'] = callback; }

正文到此结束