Array.Iterator - Iterate trough your arrays

Array.Iterator.js

Array.implement({

    i: 0,

    current: function(){
        return this.valid() ? this[this.i] : null;
    },

    jump: function(i){
        if (i < 0) i = -1;
        if (i > this.length - 1) i = this.length;
        this.i = i;
        return this.current();
    },

    valid: function(){
        return (this.i >= 0 && this.i < this.length);
    },

    key: function(){
        return this.valid() ? this.i : false;
    },

    slide: function(i){
        return this.jump(this.i + i);
    },  

    reset: function(){
        return this.jump(0);
    },

    end: function(){
        return this.jump(this.length - 1);
    },

    next: function(){
        return this.slide(1);
    },

    prev: function(){
        return this.slide(-1);
    }

});

var a = [1, 2, 3, 4, 5];

while (a.valid()){
    console.log(a.current());
    a.next();
}

var i = [1, 2, 3, 4];
console.log(i);
console.log('current', i.current());
console.log('next', i.next());
console.log('next', i.next());
console.log('next', i.next());
console.log('next', i.next());
console.log('prev', i.prev());
console.log('end', i.end());
console.log('prev', i.prev());
console.log('prev', i.prev());
console.log('next', i.next());
console.log('current', i.current());
console.log('reset', i.reset());

what do you think about my class? https://gist.github.com/tlimpanont/6547770