functions.js

function Base(text) {
    return function () {
        return text
    }
}

function Derived(source, prefix) {
    var text = Base(source)

    return function () {
        return prefix + text() + prefix
    }
}

function Derived2(source, prefix, color) {
    var text = Derived(source, prefix)

    return function () {
        return color + text()
    }
}

var d = Derived('foo', '!'),
    d2 = Derived2('bar', '!', 'red'),

    assert = require('assert');

assert.equal( d(), '!foo!' );
assert.equal( d2(), 'red!bar!' );