Snippet from the Sencha Touch 2.0 framework

ST 2.0.0.js

/**
 * @class Ext.data.NodeInterface
 * This class is meant to be used as a set of methods that are applied to the prototype of a
 * Record to decorate it with a Node API. This means that models used in conjunction with a tree
 * will have all of the tree related methods available on the model. In general this class will
 * not be used directly by the developer. This class also creates extra fields on the model if
 * they do not exist, to help maintain the tree state and UI. These fields are:
 * <ul>
 * <li>parentId</li>
 * <li>index</li>
 * <li>depth</li>
 * <li>expanded</li>
 * <li>expandable</li>
 * <li>checked</li>
 * <li>leaf</li>
 * <li>cls</li>
 * <li>iconCls</li>
 * <li>root</li>
 * <li>isLast</li>
 * <li>isFirst</li>
 * <li>allowDrop</li>
 * <li>allowDrag</li>
 * <li>loaded</li>
 * <li>loading</li>
 * <li>href</li>
 * <li>hrefTarget</li>
 * <li>qtip</li>
 * <li>qtitle</li>
 * </ul>
 *
 */
Ext.define('Ext.data.NodeInterface', {
    requires: ['Ext.data.Field', 'Ext.data.ModelManager'],

    alternateClassName: 'Ext.data.Node',

    /**
     * @property nextSibling
     * A reference to this node's next sibling node. `null` if this node does not have a next sibling.
     */

    /**
     * @property previousSibling
     * A reference to this node's previous sibling node. `null` if this node does not have a previous sibling.
     */

    /**
     * @property parentNode
     * A reference to this node's parent node. `null` if this node is the root node.
     */

    /**
     * @property lastChild
     * A reference to this node's last child node. `null` if this node has no children.
     */

    /**
     * @property firstChild
     * A reference to this node's first child node. `null` if this node has no children.
     */

    /**
     * @property childNodes
     * An array of this nodes children.  Array will be empty if this node has no chidren.
     */

    statics: {
        /**
         * This method allows you to decorate a Record's prototype to implement the NodeInterface.
         * This adds a set of methods, new events, new properties and new fields on every Record
         * with the same Model as the passed Record.
         * @param {Ext.data.Model} record The Record you want to decorate the prototype of.
         * @static
         */
        decorate: function(record) {
            if (!record.isNode) {
                // Apply the methods and fields to the prototype
                var mgr = Ext.data.ModelManager,
                    modelName = record.modelName,
                    modelClass = mgr.getModel(modelName),
                    newFields = [],
                    i, newField, len;

                // Start by adding the NodeInterface methods to the Model's prototype
                modelClass.override(this.getPrototypeBody());

                newFields = this.applyFields(modelClass, [
                    {name: 'parentId',   type: 'string',  defaultValue: null},
                    {name: 'index',      type: 'int',     defaultValue: 0},
                    {name: 'depth',      type: 'int',     defaultValue: 0,     persist: false},
                    {name: 'expanded',   type: 'bool',    defaultValue: false, persist: false},
                    {name: 'expandable', type: 'bool',    defaultValue: true,  persist: false},
                    {name: 'checked',    type: 'auto',    defaultValue: null},
                    {name: 'leaf',       type: 'bool',    defaultValue: false, persist: false},
                    {name: 'cls',        type: 'string',  defaultValue: null,  persist: false},
                    {name: 'iconCls',    type: 'string',  defaultValue: null,  persist: false},
                    {name: 'root',       type: 'boolean', defaultValue: false, persist: false},
                    {name: 'isLast',     type: 'boolean', defaultValue: false, persist: false},
                    {name: 'isFirst',    type: 'boolean', defaultValue: false, persist: false},
                    {name: 'allowDrop',  type: 'boolean', defaultValue: true,  persist: false},
                    {name: 'allowDrag',  type: 'boolean', defaultValue: true,  persist: false},
                    {name: 'loaded',     type: 'boolean', defaultValue: false, persist: false},
                    {name: 'loading',    type: 'boolean', defaultValue: false, persist: false},
                    {name: 'href',       type: 'string',  defaultValue: null,  persist: false},
                    {name: 'hrefTarget', type: 'string',  defaultValue: null,  persist: false},
                    {name: 'qtip',       type: 'string',  defaultValue: null,  persist: false},
                    {name: 'qtitle',     type: 'string',  defaultValue: null,  persist: false}
                ]);

                len = newFields.length;

                // We set a dirty flag on the fields collection of the model. Any reader that
                // will read in data for this model will update their extractor functions.
                modelClass.getFields().isDirty = true;

                // Set default values
                for (i = 0; i < len; ++i) {
                    newField = newFields[i];
                    if (record.get(newField.getName()) === undefined) {
                        record.data[newField.getName()] = newField.getDefaultValue();
                    }
                }
            }