数组的操作
let arr1 = [1,2,3];
let arr2 = [4,5,6];
let arr = arr1.concat(arr2);//arr = [1,2,3,4,5,6];
arr1.push(arr2);
console.log(arr1);输出 [1,2,3,[4,5,6]]
但是开始我是赋值给arr3
let arr1 = [1,2,3];
let arr2 = [4,5,6];
let arr = arr1.concat(arr2);//arr = [1,2,3,4,5,6];
arr3=arr1.push(arr2);
console.log(arr3)
但是输出的是数字6(number)
原因就是arr.1.push(arr2) 输出是number类型,返回数组长度