Ext is used to develop the UI of the web application. This framework is based on JavaScript; it inherits all the features of JavaScript along with its own features. It is also used to create desktop applications. It provides dual features. All modern web browsers support it, like Chrome, Safari, and FF. It is also supported on mobile devices by the product name Sencha. The latest version of Ext is used for mobile and desktop applications, with no code differences between the two platforms; this is the 6th version. It is MVC/MVVM based architecture.
Jack Slocum created the first version of Ext JS, Ext JS 1.1, in 2006. It had a set of various utility classes for various purposes; it was an extension of YUI. It was named as a YUI-ext library.
- Ext JS 2.0 was released in 2007. It had new API documentation for desktop applications with limited features and functionality. This version doesn’t have backward compatibility with earlier versions of Ext JavaScript.
- Ext JavaScript 3.0 was released in 2009. It introduced many new features, such as charts and list views, but it was not very fast. It had backward compatibility with its previous version, 2.0.
- Ext JavaScript version 4.0 was released in 2011. This version has a completely revised structure, following the model-view-controller architecture and improving speed.
- Ext JavaScript 5.0 was released in 2014. Ext JS 5.0 introduced the MVVM architecture, two-way data binding, responsive layouts, touch support, and improved performance for cross-platform applications.
- Ext JS 6.0 was released in 2015, combining desktop and mobile capabilities through the Classic and Modern toolkits, allowing developers to build applications with a common framework.
- Ext JavaScript 7.1–7.9 (2020–2025). Ext JS 7.x focused on stability, security, performance, accessibility, modern browser support, updated themes, improved grids, and enterprise application maintenance.
Sencha CMD
To do code modification of EX JavaScript code, Sencha CMD is a tool provided by Sencha, which helps with
scaffolding and production build generation.
Sencha Inspector
In Sencha, to debug the application while developing, Sencha Inspector is used as a debugging tool that helps a developer to debug in a smooth way.
Sencha IDE Plugins
If you are looking for a job related to ExtJS, you need to prepare for the 2026 ExtJS Interview Questions. Every interview is different for different job profiles, but to clear the interview, you still need to have a good, clear understanding of ExtJS. Here, we have compiled important ExtJS Interview Questions and Answers to help you succeed in your interview.
In this 2026 ExtJS Interview Questions article, we shall present the 15 most important and frequently used ExtJS interview questions. These questions will help students build their understanding of ExtJS and ace the interview.
ExtJS Interview Questions (Basic)
This first part covers basic Interview Questions and Answers.
Q1. What is Ext JS, and what is the name of the library on which it is based?
Answer:
It is a JavaScript framework to develop rich UI web-based desktop applications. Ext JS stands for extended JavaScript. It is a Sencha product extended from YUI (Yahoo User Interface).
Q2. What is the difference between Ext JS and jQuery?
Answer:
These are the basic Ext JS interview questions. Both frameworks are quite different; we can compare Ext JS and jQuery UI, as Ext JS is a full-fledged, UI-rich framework. But still, Ext JS has many more components than jQuery UI.
JQuery is a lightweight JavaScript library mainly used for DOM manipulation, event handling, animations, and AJAX operations. Ext JS provides more built-in components like grids, forms, charts, and dashboards, while jQuery usually requires additional plugins for advanced UI features
Q3. What is ViewModel in MVVM architecture?
Answer:
A ViewModel acts as a bridge between the View and the Model. It manages application data, supports two-way data binding, and automatically updates the UI whenever the underlying data changes, reducing the need for manual synchronization.
In the MVVM architecture, the MVC controller is replaced by a ViewModel.
ViewModel: − It is responsible for mapping between views and models.
It is responsible for wrapping the model’s data for the view. It does so without any interaction with the UI view. It has only the model’s knowledge.
Let us move to the next ExtJS Interview Questions.
Q4. What is the use of Ext.onReady()?
Answer:
Ext.onReady() is the first method that is called when the DOM is fully loaded, so that whatever element we want to refer to will be available when the script runs. Ext.onReady() executes a function after the HTML document has been fully loaded and the DOM is ready. It ensures that all page elements are available before any Ext JS components or scripts are initialized.
Q5. Program to write before and after load events in the store?
Answer:
grid.getStore().on ({
beforeload : function(store) {
// do whater operation needed as per requirments
},
load : {
fn : function(store) {
// do whatever operation needed as per requirements
},
scope : this
}
store.load();
});
ExtJS Interview Questions (Advanced)
Let us now have a look at the advanced Interview Questions and Answers.
Q6. Explain renderer and its use?
Answer:
A renderer formats or customizes the display of data before it appears in a grid or other component. It can change text, apply styles, display icons, or format dates and numbers without modifying the original stored data.
A renderer is used when we want to manipulate the data that we get from the store to show manipulated data based on some criteria.
It is a column property that can be used as: –
renderer: function(value, metadata, record, rowIndex, colIndex, store){
// logic to perform operation
}
Q7. What are all the layouts in Ext JS?
Answer:
Different types of layouts are in Ext JS −
- Border Layout
- Fit Layout
- VBox Layout
- HBox Layout
- Card Layout
- Accordion Layout
- Anchor Layout
- Column Layout
- Table Layout
- Absolute Layout
- Auto Layout
Each layout is designed for different interface requirements.e
Q8. Explain vType in Ext JS?
Answer:
A vType is a built-in validation mechanism used for form fields. It validates user input against predefined rules, such as email addresses, URLs, and alphanumeric values, as well as custom validation logic, helping ensure accurate data entry.
This is the validation type that can be customized easily. A few vTypes provided by Ext JS are −
- emailText: − This returns false if a text is not a valid email address.
- alphanumText: − This returns false if the text entered has any symbol other than an alphabetic or numeric value.
Q9. Explain the latest version of Ext JS and its benefits?
Answer:
The latest Ext JS releases in 2026 continue the 7.x series, focusing on performance, stability, security, and enterprise application development. They include enhancements to grids, charts, accessibility, modern browser compatibility, and developer productivity. Ext JS supports both desktop and responsive web applications through its Classic and Modern toolkits, making it suitable for building scalable, feature-rich business applications.
Q10. What are the Ext JS implementation tools?
Answer:
Ext JS development can be done using any modern code editor or IDE that supports JavaScript. Popular choices include Visual Studio Code, WebStorm, IntelliJ IDEA, Eclipse, and Sublime Text. Developers typically use Sencha Cmd to create projects, manage application resources, compile code, optimize builds, and package applications for deployment. These tools help improve productivity and simplify the overall development process.
Q11. What is a Store in Ext JS?
Answer:
A Store is a collection of records that manages application data. It loads data from local or remote sources, supports sorting, filtering, grouping, and pagination, and supplies data to UI components such as grids, combo boxes, and charts.
Q12. What are some common techniques for optimizing an Ext JS application?
Answer:
Application performance can be improved by loading data only when required, reducing unnecessary component rendering, using pagination, minimizing server requests, optimizing layouts, and removing unused resources to achieve faster response times.
Q13. What are plugins in Ext JS?
Answer:
Plugins add extra functionality to existing components without changing their core behavior. They allow developers to extend features such as editing, exporting, drag-and-drop, or validation in a reusable way.
Q14. What is the difference between local and remote sorting?
Answer:
Local sorting arranges records already available in the browser, while remote sorting sends the sorting request to the server, which returns the records in the required order. Remote sorting is preferred for large datasets.
Q15. What is the Session class in Ext JS?
Answer:
The Session class manages application data during a user’s interaction. It tracks record changes, prevents duplicate data instances, and helps synchronize updates across multiple views before saving them.
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