Top 50 Reactjs Questions
1. What is Reactjs?
React is a JavaScript library that makes building user interfaces easy. It was developed by Facebook.
2. Does React uses HTML?
No, It uses JSX, which is similar to HTML.
3. When was React first released?
React was first released on March 2013.
4. Give me two most significant drawbacks of React
Integrating React with an MVC framework like Rails requires complex configuration.
React require the users to have knowledge about the integration of the user interface into the MVC framework.
5. State the difference between Real DOM and Virtual DOM
Real DOM
It is updated slowly.
It allows a direct update from HTML.
It wastes too much memory.
Virtual DOM
It updates faster.
It cannot be used to update HTML directly.
Memory consumption is less.
6. What is Flux Concept in React?
Facebook widely uses the flux architecture concept for developing client-side web applications. It is not a framework or a library. It is simply a new kind of architecture that complements React and the concept of Unidirectional Data flow.
7. Define the term Redux in React
React is a library used for front-end development. It is a state container for JavaScript applications that should be used for the application's state management. You can test and run an application developed with Redux in different environments.
8. What is the 'Store' feature in Redux?
Redux has a feature called 'Store' which allows you to save the application's entire State in one place. Therefore all its component's States are stored in the Store so that you will get regular updates directly from the Store. The single state tree helps you to keep track of changes over time and debug or inspect the application.
9. What is an action in Redux?
It is a function that returns an action object. The action type and the action data are always stored in the action object. Actions can send data between the Store and the software application. All information retrieved by the Store is produced by the actions.
10. Name the important features of React
Allows you to use 3rd party libraries.
Time-Saving
Faster Development
Simplicity and Composable
Fully supported by Facebook
Code stability with One-directional data binding React Components
11. Explain the term stateless components.
Stateless components are pure functions that render DOM based solely on the properties provided to them.
12. Explain React Router.
React Router is a routing library that allows you to add new screen flows to your application, and it also keeps the URL in sync with what's being shown on the page.
13. What is a dispatcher?
A dispatcher is the central hub of the app where you will receive actions and broadcast payload to registered callbacks.
14. What is meant by the callback function? What is its purpose?
A callback function should be called when setState has finished, and the component is pretended. As the setState is asynchronous, which is why it takes in a second callback function.
15. Explain the term high order component.
A higher-order component also shortly known as HOC is an advanced technique for reusing component logic. It is not a part of the React API, but they are a pattern that emerges from React's compositional nature.
16. Explain yield catchphrases in JavaScript.
A presentational part is a segment that allows you to render HTML. The segment's capacity is presentational in markup.
17. What are props in Reactjs?
Props mean properties, which is a way of passing data from parent to child. We can say that props are just a communication channel between components. It is always moving from parent to child component.
18. Explain yield catchphrases in JavaScript?
The yield catchphrase is utilized to delay and resume generator work, which is known as yield catchphrase.
19. Name two types of React component
Functional Component
Class Component
20. Explain synthetic events in React js
A synthetic event is a kind of object which acts as a cross-browser wrapper around the browser's native event. It also helps us to combine the behaviors of various browsers into a single API.
21. What is React State?
It is an object which decides how a specific component renders and how it behaves. The state stores the information which can be changed over the lifetime of a React component.
22. How can you update the state in react js?
A state can be updated on the component directly or indirectly.
23. Explain the use of the arrow function in React.
The arrow function helps you to predict the behavior of bugs when passed as a callback. Therefore, it prevents bugs caused by this all together.
24. State the main difference between Pros and State.
The main difference between the two is that the State is mutable and the Pros are immutable.
25. Explain the pure components in React js.
Pure components are the faster components that can replace any component with only a render(). It helps you to enhance the simplification of the code and performance of the application.
26. What kind of information controls a segment in React?
There are mainly two sorts of information that control a segment: State and Props
- State: State information that will change, we need to utilize State.
Props: Props are set by the parent and are settled all through the lifetime of a part.
27. What is 'create-react-app'?
'create-react-app' is a command-line tool that allows you to create one basic react application.
28. Explain the use of 'key' in react list.
'Keys' allow you to provide each list element with a stable identity. The keys should be unique.
29. What are children's props?
Children's props are used to pass components to other components as properties.
30. Explain error boundaries.
Error boundaries help you to catch JavaScript errors anywhere in the child components. They are most used to log the error and show a fallback UI.
31. What is the use of empty tags?
Empty tags are used in react for declaring fragments.
32. Explain strict mode.
StrictMode allows you to run checks and warnings for react components. It runs only on development build. It helps you to highlight the issues without rendering any visible UI.
33. What are reacted portals?
Portal allows you to render children into DOM node. CreatePortalments. It helps you to share data globally between various react components.
34. What is Context?
React context helps you to pass data using the tree of react components. It helps you to share data globally between various react components.
35. What is the use of Webpack?
Webpack basically is a module builder. It mainly runs during the development process.
36. What is Babel in React js?
Babel is a JavaScript compiler that converts the latest JavaScript like ES6, and ES7 into plain old ES5 JavaScript that most browsers understand.
37. How can a browser read JSX file?
If you want the browser to read JSX, then that JSX file should be replaced using a JSX transformer like Babel and then send back to the browser.
38. What are the major issues of using MVC architecture in React?
DOM handling is quite expensive
Most of the time applications were slow and inefficient
Because of circular functions, a complex model has been created around models and ideas.
39. What can be done when there is more than one line of expression?
At that time a multi-line JSX expression is the only option left for you.
40. What is the reduction?
The reduction is an application method of handling State.
41. Explain the term synthetic events.
It is actually a cross-browser wrapper around the browser's native event. These events have interface stopPropagation() and preventDefault().
42. When should you use the top-class elements for the function element?
If your element does a stage or lifetime cycle, we should use top-class elements.
43. How can you share an element in the parsing?
Using the State, we can share the data.
44. Explain the term reconciliation.
When a component's state or props change then the rest will compare the rendered element with the previously rendered DOM and will update the actual DOM if it is needed. This process is known as reconciliation.
45. How can you re-render a component without using the setState() function?
You can use the force update () function for re-rendering any component.
46. Can you update props in react?
You can't update props in react js because props are read-only. Moreover, you can not modify props received from parent to child.
47. Explain the term 'Restructuring'.
Restructuring is the extraction process of array objects. Once the process is completed, you can separate each object into a separate variable.
48. Can you update the values of props?
It is not possible to update the value of props as it is immutable.
49. Explain the meaning of Mounting and Demounting.
The process of attaching the element to the DCOM is called mounting.
The process of detaching the element from the DCOM is called demounting.
50. What is the use of the 'props-types' library?
'Prop-types' library allows you to perform runtime type checking for props and similar objects in a recent application.
