JS module example.

gistfile1.js

PP.component = (function() {
  var currentValue = null;
  var previousValues = [];

  /**
   * Changes input values, maintaining a record of how often it has done so.
   * This is a standard doc comment, and this is how it is phrased; when in
   * doubt, write JavaDoc style.
   */
  var component = {
    getValue: function() {
      return currentValue;
    },

    setValue: function(value) {
      previousValues.push(value);
      this.currentValue = value;
    },

    undo: function() {
      this.currentValue = previousValues.pop() || null;
    }
  };

  return component;
})();

component.getValue(); // null
component.setValue(100); // value is now 100
component.setValue(200); // value is now 200
component.undo(); // value is now 100 again
component.undo(); // value is now null again

// At no point have the actual variables been exposed.