indexOf & lastIndexOf

Array.prototype.myIndexOf = function(ele,start = 0){
    for(let i = start;i < this.length;i++){
        let item = this[i]
        if(ele === item){
            return i
        }
    }
    return -1
}

Array.prototype.myLastIndexOf = function(ele,start = this.length - 1){
    for(let i = start;i > -1;i--){
        let item = this[i]
        if(ele === item){
            return i
        }
    }
    return -1
}