ExtJS Development Company

Extensible JavaScript is given as a new-age JS framework for the construction of higher-impact JS Web-based application that is easy to make and works well. Actually Ext JS was developed by the company called Sencha which is the set of tools and components to create the complex, sophisticated and interactive web applications.

Best Practices:

• Optimize Performance: Avoid frequent DOM changes. Where possible, use lazy loading for data, and use heavy components like grids only occasionally.
• Cross-Browser Testing: Simplify your application’s appearance and ensure it functions well across different browsers and devices. Tools like BrowserStack can be very helpful for cross-browser testing.

Deployment and Build Tools:

• Sencha Cmd: A console application for handling ExtJS project builds, testing, and deployment. It can build production-ready versions, minimize code, and even perform some performance tweaks.

• Deployment: Ensure that the final build of the application is compiled with Sencha Cmd and hosted on a CDN to facilitate faster content loading.

Debugging and Optimization:

• Debugging Tools: Use the browser’s developer tools (e.g., Chrome DevTools) for debugging. You can also write and use log messages with ExtJS's Ext.log() to track messages and application flow.

• Code Minification: Before launching an ExtJS app, use Sencha Cmd to minify the JavaScript resources, enhancing the app's speed.

Data Management in ExtJS:

• Model: Defines the layout of the data, including fields, validations, and relationships.
• Store: A collection that stores data and provides mechanisms for data loading, filtering, and sorting. It is tightly bound to the Model.
• Proxy: Configures how data is loaded and sent to the server (e.g., via AJAX, REST, etc.).

Event Handling:

• ExtJS provides an excellent event management system to work with various events, such as clicks, key presses, and others.

1. Comprehensive Set of Components: ExtJS boasts of offering a rich sample of ready built UI widgets such as grids, forms, charts, trees among others hence reducing the amount of time developers spend on these features. These are very flexible components and can support extensive individual relations with the users.
2. Powerful Data Handling: It provides powerful data manipulation controls such as data binding, searching, sorting, grouping and paging which is important when working with large amount data.
3. Responsive Design: ExtJS has features for responsiveness and therefore, applications are optimized to be appropriate for different Devices and Web Browsers.
4. Rich Documentation and Community Support: ExtJS is very well documented, and there is a strong community available around this framework which makes it easier for developers to solve problems or find some solutions.
5. Enterprise-Level Features: In ExtJS, there are various features such as grid editing, drag and drop, complex form, etc, which are good for large scale enterprise applications. 

1. Dependency on Sencha Ecosystem: ExtJS is bundled in the Sencha line of products so it has implications in updating and product support are largely within Sencha’s discretion. The way it is designed, developers may be stuck within this ecosystem for any long term maintainance.
2. Mobile Experience Limitations: Despite this, ExtJS has support for mobile devices, though it isn’t as optimized or as flexible as more modern frameworks such as React Native or Flutter which are built ground up for building mobile apps.
3. Heavyweight: It was found that ExtJS has a larger number of requests and response times are comparatively much higher than that of the light-weight frameworks such as React or Vue.js in small scale projects with limited UI elements.
4. Large File Size: One of the main issues of ExtJS applications is the application size – it has a great many components consequently, its size tends to be really large and it is a problem when the application needs to be loaded in slow network or weak devices.
5. Licensing Costs: Of course ExtJS is a commercial framework, which implies that in order to use ExtJS in a commercial application the user needs to purchase a license, it is relatively expensive especially for start up businesses or individual developers.