slice函数封装实现

function slice(arr,begin,end){
    //若begin不存在
    begin = begin || 0
    end = end || arr.length
    // 空数组
    let result = []
    for(i=0;i<arr.length;i++){
        if(i>=begin && i<=end){
            result.push(arr[i])
        }
    }
    return result
}

let arr = [1,2,3,4,5,6,7]
let result = slice(arr)
console.log(result)