The Y-combinator: a utility function

gistfile1.txt

// The Y-combinator: a utility function!
var Y = function Y(hof) {
  return function (x) {
    return x(x);
  }(function (x) {
    return hof(function (y) {
      return x(x)(y);
    });
  });
};
console.log([1, 2, 3, 4, 5].map(
// Wrap the higher-order function in the Y-combinator
// "factorial" is not a function's name: it's introduced as a parameter
Y(function (factorial) {
  return function (n) {
    return n <= 1 ? 1 : factorial(n - 1) * n;
  };
})));
// [ 1, 2, 6, 24, 120 ]

Note: This method allocates a new closure for every iteration, which may significantly increase memory usage. It's only here to demonstrate the possibility, but should be avoided in production. Use a temporary variable or a named function expression instead.
https://en.wikipedia.org/wiki/Fixed-point_combinator#Y_combinator