[Vlasenko Fedor]

Сформулирую задачу предельно конкретно

var obj = {
    min: 0,
    max: 0,
    __reverce: 1,
    __position: 0,
    get cur() {
        this.__position += this.__reverce
        if (this.__position == this.max || this.__position == this.min) this.__reverce *= -1;
        return this.__position;

    },
    set cur(arg) {
        this.__position = arg;
    }
};
obj.max = 10, obj.cur = 8;
console.log(obj.cur);
console.log(obj.cur);
console.log(obj.cur);