once.js

function once(fns, callback, args) {
  var c = 0;
  var len = fns.length;
  var results = [];
  fns.forEach(function(fn, i) {
    fn.apply(fn, [function(value) {
      results[i] = value;
      c++;
      if (c == len) {
        callback.apply(callback, results);
      }
    }].concat(args));
  });
}