你不知道的js代码面试题?

var b = 3 // 不加;号 控制台会报错 
 ;(function c() {
 b = 2
 console.log(b);//2
        })()

//let与var的区别 
for (var i = 0; i < 5; i++) {
 
 setTimeout(function () {
 console.log(i + ' ');//55555
        }, 100)
    }
 console.log(i);//5

 for (let i = 0; i < 5; i++) {
        setTimeout(function () {
            console.log(i + ' ');//0 1 2 3 4
        }, 1000)
    }

// 数组去重
 let arr = [1, 2, 3, 3, 3, 4, 5]
 let aa = []
 arr.forEach((v) => {
 if (!aa.includes(v)) {
 aa.push(v)
        }
    })
 console.log(aa);

//四舍五入
console.log(Math.round(-2019.5));//-2019
 console.log(Math.round(2019.5)); //2020

//求数组中的最大值
 let a = [1, 6, 3, 1]
 console.log(Math.max.apply(null, a));//6

console.log(2 < 1 < 3);//true  2<1 => 0  0<3 结果是true
    console.log(2 > 1 > 3);//false 2>1 =>1 1>3 结果是false