Generate Unique IDs, Release It When Consumed

id-gen.js

function id_generator(){
  
  var store = {};

  function release_id( id ){

    delete store[ id ]; 
  }

  function generate_unique_id(){

    var candidate_id = generate_id();

    if( !is_unique_id( candidate_id ) ){

      candidate_id = generate_unique_id();
    }
    
    store[ candidate_id ] = true;

    return candidate_id;
  }

  function is_unique_id( id ){

    return !store.hasOwnProperty( id );
  }

  function generate_id(){

    return require('uuid').v4();
  }

  return {

    create: generate_unique_id,
    release: release_id
  }
}

sample.js

var job_ids = id_generator();

// get new job id
  job_id = job_ids.create();
  
// do job
// - other ids get assigned to other jobs
// - but each job id is guaranteed to be unique

// on job completion
 job_ids.release( job_id );