George MacKerron: code blog

Today, I needed a JavaScript equivalent of Ruby’s Array#compact (which returns the array stripped of any nil values).

A standard JavaScript implementation looks like this:

Array.prototype.compact = function() {
  var x, _i, _len, _results;
  _results = [];
  for (_i = 0, _len = this.length; _i < _len; _i++) {
    x = this[_i];
    if (x != null) {
      _results.push(x);
    }
  }
  return _results;
};

But since I’m using CoffeeScript, I get this monstrosity of line-noise and distraction for free when I type this:

Array::compact = -> x for x in @ when x?

This is some of the best of CoffeeScript: array comprehensions, implicit return, the existential operator ?, and more. Taking 11 lines of JavaScript busywork and turning it into 40 pithy, elegant characters.