js基础知识入门总结

<input type="button" value="按钮" onclick="myClick()" /><input type="button" value="按钮" id="btn"/>

function myClick(){ ???????console.log("点击按钮"); ?????}document.getElementById(‘btn‘).onclick=function(ev){ ????????console.log("点击按钮"); ?}

var iNum1 = 10;var sString = "abceelf";var bFlag = true;var aNum = [1,2,3,4,5];var oObject = {name:‘marry‘,age:18};var fNumber = 10.3;

var ?iNum1 = 10;var ?sString = "baude";// + 作拼接作用，使数字转换成字符串浏览器自动转换的，取toString()方法iNum1 + sString //而 -号、*号、/号只能作运算，即将所有数据转换为数字，取Number()方法，如果不能转换则为NaNvar ?bFlag = true;//布尔值转换为数字1或0iNum1 + bFlag //把数据转换成数字var ?sString2 = “20djaog”；Number(sString2)//将数字的字符串转换为数字parseInt(sString2)//将不能转换为止parseFloat("10.2ajofg")//可以转换浮动型

var ?sString = "Hello world";sString.length ?//获取字符串长度sString.charAt(2) ??//获取字符串指定索引的字符sString.substring(start,end) ??//截取字符串从start位置到end位置，如果end缺省则到结尾sString.substr(start,length) ?//截取字符串从start位置截取length个字符sString.indexOf(‘a‘,start) ?// 返回字符串中指定的字符a第一次出现的位置，若无则返回-1；若第二个参数有，则从第二个参数start的位置开始sString.lastIndexOf(‘a‘,start) ??//从右边到左边查询

//数组声明var ?aTeam = new Array(4);aTeam[0] = "dkop";......var aTeam = ["dd","es","ag"];//数组方法aTeam.toString(); //默认通过逗号隔开aTeam.join("_").toString(); ?//指定通过 _ 隔开aTeam.reverse().toString() //反序处理//字符串处理为数组var ?sString = "deig_taig_kie_lieng";sString.split("_") ?//通过指定字符进行分割，返回一个数组

if(条件1){ ???//第一种情况}else if(条件2){ ???//第二种情况}else{ ???//剩余情况}//if语句也可以使用三元运算符等价代替if(a>b){ ???c=a;}else{ ???c=b;} ???等价于 ?c = ?a>b ? a:b;

// =是赋值// ==是不判断类型，会自动转换为相同的类型再进行判断// ===会先判断类型是否相同var iNum = 10；var sNum = ‘10’；if（iNum == sNum）{ ???//不判断类型}if（iNum === sNum）{ ????//判断类型}//逻辑运算符 &&、 ?||、 ?！

//while循环var i = 0;var iSum = 0;while(i<101){ ????//当前的iSum=上次的iSum+当前的i ????iSum += i; ????i++}alert(iSum);//do...while循环

//for循环var iSum = 0;for(var i=0;i<101;i++){ ???iSum += i;}

//9*9乘法表，首先最重要的就是确定各个循环变量的范围// var i ???(1~9) ??????var j<ivar sHtml = "<table>";for(var i = 1;i<=9;i++){ ??sHtml+="<tr>"; ???for(var j = 1;j<=i;j++){ ???????sHtml+="<td>"+i+"*"+j+"="+i*j+"</td>"; ????}}sHtml+="</table>";document.writeln(sHtml);//以下是反向写入页面中var sHtml = "<table>";for(var i = 9;i>=1;i--){ ???sHtml+="<tr>"; ???for(var j = i;j>=1;j--){ ???????sHtml+="<td>"+i+"*"+j+"="+i*j+"</td>"; ???}}sHtml+="</table>";document.writeln(sHtml);

//冒泡排序：前面的元素依次和后面的元素进行比较 ???var aNumber = [10,2,34,4,56,12,45,44,6,12,23,55]; ???var iNum = 0; ???for(var i = 0;i<=aNumber.length-2;i++){ ???????for(var j = i+1;i<=aNumber.length-1;j++){ ???????????if(aNumber[i]>aNumber[j]){ ???????????????iNum = aNumber[i]; ???????????????aNumber[i] = aNumber[j]; ???????????????aNumber[j] = iNum; ???????????} ???????} ???} ???alert(aNumber);//以下是降序 ???var aNumber = [10,2,34,4,56,12,45,44,6,12,23,55]; ???var iNum = 0; ???for(var i = 0;i<=aNumber.length-2;i++){ ???????for(var j = i+1;i<=aNumber.length-1;j++){ ???????????if(aNumber[i]<aNumber[j]){ ???????????????iNum = aNumber[i]; ???????????????aNumber[i] = aNumber[j]; ???????????????aNumber[j] = iNum; ???????????} ???????} ???} ???alert(aNumber);

 ???switch(num){ ???????case 1: ???????????alert(‘星期1‘); ???????????break; ???????case 2: ???????????alert(‘星期2‘); ???????????break; ???????case 3: ???????????alert(‘星期3‘); ???????????break; ???????case 4: ???????????alert(‘星期4‘); ???????????break; ???????default: ???????????alert("星期天"); ???????????break; ???}

 ???function myClick() { ???????var iSum = 0; ???????for(var i=1;i<101;i++){ ???????????if(i==5){ ???????????????//跳出整个循环体，只加到5 ???????????????// break; ???????????????//跳过当前条件的循环，即除去5 ???????????????// continue; ???????????????//结束整个方法体，此外return也可以作为函数的返回值 ???????????????return; ???????????} ???????????iSum += i; ???????} ???????alert(iSum); ???}

 ???Math.PI; ???Math.max(10,32,40); ???Math.min(10,32,40); ???Math.round(12.59);//四舍五入 ???Math.ceil(12.1);//向上取整 ???Math.floor(12.9);//向下取整 ???Math.random();//获取0~1的随机数，不包括0和1 ???Math.floor(Math.random()*100+1) //获取1~100之前的整数

 ???var myData = new Date(); ???myData.getFullYear(); ???myData.getMonth()+1;//月是从0开始的，所以要加1 ???myData.getDay(); ???myData.getHours(); ???myData.getMinutes(); ???myData.getSeconds();

 ???function myClick() { ???????var i=0; ???????//循环执行 ???????var timer = setInterval(function () { ???????????i++; ???????????if(i==6){ ???????????????//清除指定的定时器 ???????????????clearInterval(timer); ???????????} ???????????console.log(i); ???????},1000); ???????//只执行一次 ???????setTimeout(function () { ???????????i++; ???????????console.log(i); ???????},1000); ???}