4-4 while 语句

1，while

 while(表达式){
    代码块
} 
表达式为true, 会一直执行while中的代码块

var a = 0;
while (a <= 3) {
    //只要a<=10为true就一直循环
    alert(a);
    a++;
}

2 do—-while(了解)
tips：即便不满足条件，循环体也会先执行一遍

do{
  循环体
}while(循环条件)

var a = 0;
do {
    console.log(a)
    a++;
} while (a <= 3)