if 判断

let score=162;

if(score>=80){
    alert("优秀");
}else if(score>=60){
    alert("及格");
}else{
    alert("不及格");
}

三元运算符

let a=110;
let b=20;
let max_num = a>b ? a : b;
alert(max_num);

循环结构

while 循环

let a=10;
while(a>=0){
    console.log(a);
    a-=2;
}

for 循环

for(let i=1;i