3.2、控制语句

3.2.1、if

if (boolean) { //boolean为true的情况下才会走{}中内容 }

var a = 10;
        var b = 20;
        if(a>b){
           console.log("yes")
        }
        {
           console.log("no")
        }

3.2.2、if else

if (boolean) { boolean true } else { boolean false }

var age=23;
        if(age>=22){
            console.log("步入婚姻的殿堂")
        }
        else{
            console.log("一个人爽")
        }

3.2.3、if else-if else

 var age =20;
        if(age >=18 ){
            console.log("成人")
        }
        else if(age >= 12){
            console.log("青少年")
        }
        else if(age >= 6){
            console.log("少年")
        }
        else{
            console.log("小屁孩")
        }

3.2.4、while

while (boolean ) { //boolean true (一直执行) 陷入一个死循环 }

 var a = 10;
        while(a){
            alert("hello world");
        }

3.2.5、while-for

var a = 0;
        while(a<=2){
            console.log(a);
            a++;
        }

3.2.6、for

 for(a=0;a<=2; a++){
            console.log(a);
        }

3.2.7、fon-in

 var obj = {
            name:"he",
            age:18,
            skill:"js"
        }
        for(var item in obj){
            console.log(obj)
        }

3.2.8、break/continue

break 达到某个条件跳出（中断）循环

 for(var i=0;i<=6;i++){
            console.log(i);
            if(i==3){
                break;
            }
            console.log("hello world");
        }

3.2.9、continue 跳过某个元素继续循环

 for(var i=0;i<=6;i++){
            if(i==3){
                continue;
            }
            console.log(i);
        }

3.2.10、 switch

switch(多分支选择语句)

        var x = "男";
        switch(x){
            case"男":
               console.log("男");
            break;
            case"女":
               console.log("女");
            break;
            default:
               console.log("其他")
        }