Data binding is a facility provided by a number of UI frameworks. The data source is bound to the UI controls, which display the data in a predefined format. Ext JS 4 provides a rich set of controls that display the data fetched from different sources. The data source is wired to the UI controls that automatically process the data and display it in appropriate format. These controls update themselves whenever the data changes. The controls that are bound to the data sources usually include data grids, trees, and so on.