数组的浅拷贝

const arr1 = [1,2,3];
const arr2 = arr1.slice();
console.log(arr2); //[ 1, 2, 3 ]

const arr1 = [1,2,3];
const arr2 = arr1.slice(2, 3);// 左闭右开
console.log(arr2); //[ 3 ]

const arr1 = [1,2,3];
const arr2 = [0,1,2].concat(arr1);
console.log(arr2); //[ 0, 1, 2, 1, 2, 3 ]

const arr1 = [1,2,3];
const arr2 = [].concat(arr1);
console.log(arr2);// [ 1, 2, 3 ]