Join

Join.js

/**
 * Join
 *   Joins async callbacks with arguments concatenated.
 * Usage:
 *   var join = new Join;
 *   getScore (angel, buffy, join());
 *   getNextMatch (angel, join());
 *   recordVisitAndGetInfo (angel, buffy, join());
 *   join.after = function(score, next, vinfo) {
       if (this.score > 0.9 && ! this.vinfo.last_visit) {
         sendVisitorEmail(angel, buffy);
       }
       doSomeFinalThings(score, next, vinfo);
 *   };
 */
function Join() {
  var waitingFor = 0, args = [];
  return function() {
    var argIndex = waitingFor;
    waitingFor += 1;
    return function() {
      args[argIndex] = arguments;
      waitingFor -= 1;
      if (waitingFor === 0)
        join.after.apply(null, args.reduce(__apply_concat, []));
    };
  };
}
var __apply_concat = Function.apply.bind([].concat);
//equivalent to function(concatedArgs, args){ return [].concat.apply(concatedArgs, args); }