A cacheable JSON Store using sessionStorage for Ext JS 3.4.x.x

CacheableJsonStore.js

Ext.namespace('COMPANYNAME.data');

COMPANYNAME.data.CacheableJsonStore = Ext.extend(Ext.data.Store, {
  
	storageKeyName: null,	// (string) sessionStorage key name

	constructor: function (config) {

		Ext.data.JsonStore.superclass.constructor.call(this, Ext.apply(config, {
			reader: new Ext.data.JsonReader(config)
		}));
		
		this.on('beforeload', function (store, options) {
			// 1. The client must implement sessionStorage
			// 2. The developer must assign a key name to the store
			if(!window.sessionStorage || !this.storageKeyName)
				return true;

			// Avoid a server request/response by retrieving a JSON string from sessionStorage
			var jsonData = window.sessionStorage.getItem(this.storageKeyName);
			if(!jsonData)
				return true;

			// Try to construct an object from the JSON string
			var jsonObject;
			try {
				jsonObject = Ext.decode(jsonData);
			}
			catch(e) {
				return true;
			}
			
			// Avoid using empty objects created from an empty JSON string
			if(!jsonObject)
				return true;

			// Populate this store with the jsonObject
			this.loadData({data: jsonObject});

			// Return false to cancel the load() action
			return false;
		}, this);

		this.on('load', function (store, records, options) {
			// 1. The client must implement sessionStorage
			// 2. The store, records, and data objects must be initialized
			// 3. The developer must assign a key name to the store
			if (!window.sessionStorage || !store || !records ||
				!store.reader.jsonData.data || !this.storageKeyName)
				return;

			// Do not store data for failed JSON requests
			if (store.reader.jsonData.success == false)
				return;
			
			// Try to construct a JSON string from the object
			var jsonString;
			try {
				jsonString = Ext.encode(store.reader.jsonData.data);
			}
			catch(e) {
				return;
			}
			
			// Do not store empty, null, or undefined JSON "strings"
			if(!jsonString)
				return;

			// Assign the JSON string to the key name in sessionStorage
			window.sessionStorage.setItem(this.storageKeyName, jsonString);
		}, this);
	}
});

Ext.reg('cacheablejsonstore', COMPANYNAME.data.CacheableJsonStore);