Instead of this:

  var mapArgs = function() {
    var args = Array.prototype.slice.call(arguments, 0, arguments.length - 1);
    var mapper = Array.prototype.slice.call(arguments, arguments.length - 1);
    return args.map(mapper);
  };

  var mapArgs = function(...args, mapper) {
    return args.map(mapper);
  };

  var max = Math.max.apply(null, [1, 2, 3, 4]);

  var max = Math.max(...[1, 2, 3, 4]);

http://stackoverflow.com/questions/2856059/passing-an-array-...

http://stackoverflow.com/questions/1316371/converting-a-java...

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

I'm still learning more about JS and so I'm no expert, but it seems to be similar in concept to use the ... in other languages. I think Groovy has something similar and Java has the varargs. They have obvious differences, but conceptually I think of it as passing in a variable number of args.