SOURCE

Array.prototype.myslice =  function(start,end){
    if(start&&end){
        start = start<0?start = this.length+start:start
        end = end<0?end = this.length+end:end
    }
    if(!start) start = 0
    if(!end) end = this.length
    let res=[];
   
    for(let i=start;i<end;i++){
        res.push(this[i])
    }

    return res
}


const arr = [1,2,3,4,5,6,7,8,9]

console.log(arr.myslice(4,7))
console.log(arr.myslice(-4,-2))
console.log(arr.myslice(2))


String.prototype.myslice =  function(start,end){
    if(start&&end){
        start = start<0?start = this.length+start:start
        end = end<0?end = this.length+end:end
    }
    if(!start) start = 0
    if(!end) end = this.length
    let res =''
   
    for(let i=start;i<end;i++){
        res +=this[i]
    }

    return res
}

const str = 'hello javascript'

console.log(str.myslice(4,9))
console.log(str.myslice(-6,-3))
console.log(str.myslice(3))