less.js/test/browser/runner-main-options.js

var less = {};
less.functions = {
  add: function(a, b) {
    return new(less.tree.Dimension)(a.value + b.value);
  },
  increment: function(a) {
    return new(less.tree.Dimension)(a.value + 1);
  },
  _color: function(str) {
    if (str.value === "evil red") {
      return new(less.tree.Color)("600");
    }
  }
};