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); // objectconsole.log(str instanceof String);console.log(str.constructor == String);console.log(Object.prototype.toString.call(str) === "[object String]"); // truevar str1 = "abcd";console.log(typeof str1); // stringconsole.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;}