function idGenerator() {

    this.counter = 1000;

    this.generate = idGenerator.generate;

}

​

idGenerator.generate = function() {

    return (this.counter++).toString(16);

};

​

var userIdGenerator = new idGenerator();

var roomIdGenerator = new idGenerator();

​

console.log(userIdGenerator.generate());

console.log(userIdGenerator.generate());

​

console.log(roomIdGenerator.generate());

console.log(roomIdGenerator.generate());

console.log(userIdGenerator.generate == roomIdGenerator.generate);