combine.js

function combine() {
  var funcs = Array.prototype.slice.call(arguments, 0);
  return function(obj) {
    var _this = this;
    return funcs.reduce(function(v, func) {
      return func.call(_this, v);
    }, obj)
  }
}

// Now this
[1,2,3,4]
  .map(function plusOne(i) {
    return i+1;
  })
  .map(function timesTwo(i) {
    return i*2;
  });

// can be rewritten as
[1,2,3,4]
  .map(combine(function plusOne(i) {
    return i+1;
  },
  function timesTwo(i) {
    return i*2;
  }));