1.if语句
语法:if(条件){
条件成立时执行
}else{
条件不成立执行
}
例
var ji ?= 20; ???????if(ji>=20){ ???????????console.log(‘恭喜你，吃鸡成功，大吉大利‘) ???????}else{ ???????????console.log(‘很遗憾 下次继续努力‘) ???????????????????}2.switch语句
语法:switch(值){
case 值1:
执行语句
break;
case 值:
执行语句
break;
}
???<script type="text/javascript"> ???????//switch ("better") 表示条件.case表示符合条件后执行的语句 ???????switch ("better0") { ???????????case "good": ???????????????console.log("玩的不错") ???????????????break; ???????????case "better": ???????????console.log("玩的非常好") ???????????????break; ???????????case "best": ???????????console.log("吃鸭子啦") ???????????????break; ???????????default: ???????????????console.log("玩的真菜") ???????????????break; ???????} ???????????</script>3while和do while语句
while语法:
while(条件){
执行代码块
}
???<script type="text/javascript"> ???????//whilex循环 ???????????????//1.初始化循环变量 2.判断循环条件 ?3、更新循环变量 ???????var i = 1; ?//1.初始化循环变量 ???????????????while(i<=9){ ??//2.判断循环条件 ?// ???????????console.log(i) ???????????????????????i = i+1; //3、更新循环变量.切记这三步 ???????} ???????????????//练习 ???????????????//将 1-100之间的所有是3的倍数 输出出来 ???????var j = 1; ???????while (j<=100){ ???????????if(j%3===0){ ???????????????console.log(j) ???????????} ???????????j++; ???????????????????} ???????????</script>do while语法
注意:do while 会先执行一次do后面的代码块,然后再进行while条件判断的.
do{
执行代码块
} while (条件);
<script type="text/javascript"> ???????//while 循环三部曲 ???????//1.初始化变量 ??2.判断循环条件 ??3.更新循环变量 ???????//不管while条件是否成立,都会先运行一次do里面的代码,然后再去进行while判断. ???????var i = 5; ???????do{ ???????????console.log(i) ???????????i++; ???????} while (i<10); ???</script>4 for语句
语法:
//for (var 1=10 初始化变量,i>=1是条件,i--是更新变量.每个语句间使用;隔开)
for (var i = 10; i>=1; i--) {
console.log(i)
}
???<script type="text/javascript"> ???????//for (var 1=10 初始化变量,i>=1是条件,i--是更新变量.每个语句间使用;隔开) ???????for (var i = 10; i>=1; i--) { ???????????console.log(i) ???????} ???????//输出1-100间的偶数 ???????for (var i = 1; i <= 100; i++) { ???????????if (i%2==0){ ???????????????console.log(i) ???????????} ???????} ???????//计算1-100之间所有数的和 ???????// var sum=0 ???????// for (var i = 1; i <= 100; i++) { ???????// ????sum+=i ???????// }console.log(sum) ???????// for (var i = 1; i <=3; i++) { ???????// ????for (var x =1; x <=6; x++) { ???????// ????????document.write("*") ???????????????????????// ????}document.write("<br>") ???????????????????// } ???????????</script>数组:
???<script type="text/javascript"> ???????/* 数据的创建方式: ???????1.字面量方式 ???????2.函数构造法 ???????*/ ???????//字面量方式,推荐这种方式.因为简单明了 ???????var colors =["red","green","blue"]; ???????console.log(colors) ???????// 使用构造函数 new ???????var ?colors2 = new Array("balck","white","origin"); ???????console.log(colors2) ???????//数组赋值 ???????var arr1 = []; ???????arr1[0] = "www.google.com"; ???????arr1[1] = "wwww.it.com"; ???????arr1[2] ="www.sohu.com"; ???????arr1[3] ="www.sina.com"; ???????arr1[4] ="www.163.com"; ???????// console.log(arr1) ???????for (var i = 0; i <arr1.length; i++) { ???????????console.log(arr1[i]) ???????} ???</script><script type="text/javascript"> ???????//数组的合并 concat ???????// var north =["河南","北京","河北"]; ???????// var south =["上海","苏州","杭州"]; ???????// var newArr = north.concat(south); ???????// console.log(newArr) ???????//转换成字符串 toString() 直接转换成字符串,用逗号隔开 ???????var score=[100,33,56,67,87]; ???????var str = score.toString(); ???????console.log(str) ???????//join()方法,使用指定的字符串分割数组 ???????var str2 = score.join("|"); ???????console.log(str2) ???????//indexOf() 查指定字符串的下标,指的是正向查找 ???????var index = score.indexOf(67); ???????var index1 = score.indexOf(99); //查找的不在数组中,返回-1 ???????console.log(index) ???????console.log(index1) ???????// lastindexOf(),倒叙查找.注意.正向和反向查找的索引值都是一样的. ???????var index2 ?=score.lastIndexOf(67); ???????console.log(index2) ???????//数组排序之反转数组,原数组也会被反转 ???????var names =["alne","jack","chen","wang","liu","ago"]; ???????var reverseName = ?names.reverse(); ???????console.log(reverseName) ???????console.log(names) ???????//按照英文字母排序,如果第一个字符相同,按照后面一个字母排列,以此类推 ???????var names1 = names.sort(); ???????console.log(names1) ???????//移除第一个元素. ???????var frist = names.shift(); ???????console.log(frist) ???????console.log(names) ???????//unshift() 添加一个或多个值,并返回数组的长度. ???????var names2 = names.unshift("pinjin","xuehua","xiaohei"); ???????console.log(names) ???????console.log(names2) ???????//push(),pop() 添加,删除 ???????//push() 默认添加到数组的最后 ???????var names3 = names.push("lirui","xiaoxiao"); ???????console.log(names) ???????console.log(names3) ?//返回新的长度 ???????//pop()删除默认从最后一个开始删除,names4是被删除的元素 ???????var names4 =names.pop(); ???????names.pop(); ???????names.pop(); ???????console.log(names4) ???????// 分割,反转字符串"hello luffy" ???????var a = "hello luffy"; ???????// var x = a.split(" ") ???????console.log(a.split("").reverse()) ???</script>函数:
???<script type="text/javascript"> ???????????????//js中函数是声明是用function funcname(),有函数的声明,就一定有调用. ???????function add(){ ???????????alert("函数被调用了") ???????} ???????add() ???????//声明带形参的函数 ???????function add2(x,y){ ???????????alert(x+y) ???????} ???????add2(4,7) ???????//带返回值的函数 ???????function add3(a,b){ ???????????return a*b ???????} ???????// console.log(add3(5,9)) ???????alert(add3(5,10)) ???</script>js02-常用流程控制语句
原文地址：https://www.cnblogs.com/lovepy3/p/9517278.html