数组合并
- concat
- slice+push.apply
- slice+push
concat
function concat(arr1, arr2) {return arr1.concat(arr2)
}
slice+push.apply
function concat(arr1, arr2) {let newArr=arr1.slice(0);[].push.apply(newArr,arr2)return newArr
}
slice+push
function concat(arr1, arr2) {let newArr=arr1.slice(0);arr2.forEach(item=>{newArr.push(item)})return newArr
}