修改数组长度

splice

修改原数组

const arr = [1,2,3]
arr2 = arr.splice(0,1)

console.log(arr) // [2, 3]
console.log(arr2) // [1]
console.log(arr2.length) // 1

不修改原数组

const arr = [1,2,3]
arr2 = arr.slice(0,1)

console.log(arr) // [1, 2, 3]
console.log(arr2) // [1]
console.log(arr2.length) // 1

var arr = [1, 2];
arr.length = 4;    //大于原有长度
console.log(arr); //输出结果:(4) [1, 2, empty x 2]

var arr = [1, 2, 3, 4];
arr.length = 2;    //小于原有长度
console.log(arr);  //输出结果: (2) [1, 2]