function whenAllTriggered(tokens, callback) {
  
  // returns a function that takes a single token
  // once this function has been called with all tokens at least once,
  // callback is invoked.
  
  var triggeredStates = {},
      nTokens = 0,
      nTriggered = 0;
    
  for(var i = 0; i < tokens.length; i++) {
    triggeredStates[tokens[i]] = false;
    nTokens++;
  }
  
  // trigger function
  return function (token) {
    if (triggeredStates[token] === false) {
      triggeredStates[token] = true;
      nTriggered++;
      if (nTriggered == nTokens) {
        callback();
      }
    }
  };

};


var trigger = whenAllTriggered(["ONE", "TWO", "THREE"], function () {
  console.log("Partaaaay!");
})

trigger("ONE");
trigger("THREE");
trigger("TWO"); // logs "Partaaaay!"