19 Best React Interview Questions Answers - Algrim.co

19 Best React Interview Questions Answers - Algrim.co div Is perfectly valid JSX syntax. Notice that we are using native javascript directly within our template; this is what makes JSX a powerful tool within React. 14. What is one tool that helps debug React applications, and how? React dev tools is a great tool for analyzing and debugging React applications. It can be used as an add-on to the standard Chrome or Firefox developer tools, and it provides unique interfaces and interactions for exploring the structure of your React component tree and the internal state and props being used to display data to your users. In React dev tools, a user can make changes to various pieces of application state in their components to view outcomes on the UI, and they have an easily navigable interface for traversing the tree structure of their React application. 15. Explain the lifecycle method componentWillUnmount(); componentWillUnmount() is another React component life-cycle method. Unlike componentDidMount(), which is executing directly after the component is rendered to the DOM. componentWillUnmount() is executed directly before your React component is removed from the DOM. This method is often used to clean up event bindings or interval functions (that were often set in the componentDidMount lifecycle method). 16. What does React mean by saying the React framework is the “V” in MVC? React is only intended to handle the rendering of the visual layer of your application. For this reason, it is compared to the View in a traditional Model-View-Controller application. In a practical sense, this means that React components are not intended to handle responsibilities like fetching data from an API, holding/maintaining the full application state, or executing algorithmic logic. For those types of responsibilities, React recommends using a state container library like Redux. 17. Explain Prop Types. Prop Types are a way for a developer to declare the data type of an argument (prop) that is passed to a React component. When declaring the Prop Types for a React component, the developer can declare that a prop must be one of the primitive Javascript types like String, Number, Array, or Object for example, or, the developer can also create their own custom data types and declare those as Prop Types for components. Props can also be declared as required or optional, and defaults can be provided for Props. Using Prop Types is intended to provide some of the benefits to a full type system like that in Java or C++. 18. Is the following a valid return value for a React component’s render() method? `divHello/divdivWorld/div`. In all but the most recent versions of React, this is not a valid return value for a React component, because there is no wrapper element surrounding the two adjacent div elements. The latest versions of React (post mid-2018, > version 16) have started adding support for adjacent elements with no wrapper. 19. When is the `key` attribute used in React? What can happen if it is not used? The `key` attribute should be added to list elements in React components when the component is responsible for iterating over some iterable object and rendering an element to the DOM for each iteration. React uses the `key` attribute internally when running its reconciliation algorithm in order to decide which elements on the screen need to be re-rendered. Neglecting to use the `key` attribute on list elements can lead to unexpected and incorrect rendering behavior, and will cause warnings to be thrown in the developer console.