清空数组

直接修改 length

const arr = [1, 2, 3]
arr.length = 0
console.log(arr) // []

使用 splice()

const arr = [1, 2, 3]
arr.splice(0, arr.length)
console.log(arr) // []

重新赋值

let a = [1, 2, 3]
let b = a
a = []
console.log(b) // [1, 2, 3]，b 仍然指向旧数组