REACT Practice Test 1 — Questions and Answers

Question 1: Which of the following React functions will update the data of a component while remaining within the componentWillMount?

updateState()
initState()
addState()
setState() (Correct answer)

Correct answer: setState()

The `setState()` function is the primary way to update a component's state in React, triggering a re-render. While `componentWillMount` is a legacy lifecycle method called before the component mounts, calling `setState()` within it allows you to update the component's state before the initial render, ensuring the component mounts with the desired data. However, for new code, `constructor` for initial state or `componentDidMount` for data fetching is generally preferred.

Question 2: What does React not include?

Any form of a data layer
An event system (other than vanilla DOM events)
Any AJAX capabilities whatsoever
All of the above (Correct answer)

Correct answer: All of the above

React is a library primarily focused on building user interfaces, specifically the 'V' in MVC. It intentionally does not include features like a built-in data layer (leaving that to state management libraries like Redux), its own AJAX capabilities (relying on standard JavaScript APIs like `fetch` or `axios`), or a comprehensive event system beyond synthetic DOM events. This modularity allows developers to choose their preferred tools for these concerns.

Question 3: Which step should be completed first when configuring Gulp on a developer machine?

Import modules
Create a folder structure
Define a gulpfile.js (Correct answer)
Launch a local server

Correct answer: Define a gulpfile.js

When setting up Gulp, the first essential step after installing Gulp globally and locally is to create a `gulpfile.js` file in your project's root directory. This file is where you define all your Gulp tasks, specifying what operations Gulp should perform, such as compiling SASS, minifying JavaScript, or running a local server. Without this file, Gulp has no instructions to execute.

Question 4: Which JavaScript API may be used to delete an item from a Flux store's private storage?

Lodash (Correct answer)
Toastr
Strict
ExtendedJSArrayAPl

Correct answer: Lodash

Lodash is a popular JavaScript utility library that provides a wide range of helper functions for common programming tasks, including manipulating arrays and objects. While Flux stores manage their own state, Lodash functions like `_.omit` or `_.without` can be used within a store's logic to immutably remove items from its private data structures, making it a useful tool for state management operations within the store.

Question 5: For type verification in React components, what property name is used?

propTypes (Correct answer)
propertyTypesChecking
propertyTypes
propTypesChecking

Correct answer: propTypes

In React, `propTypes` is a special static property used within a component definition to specify the expected data types for the props it receives. This mechanism helps with type checking during development, providing warnings in the console if props don't match the defined types. It's a valuable tool for ensuring component reliability, maintainability, and clear communication of component interfaces.

Question 6: In the following code segment, select the reason for adding code to the index.js file - S = jQuery= require("jquery");

Bootstrap expects 'JQuery to be in the path provided
Bootstrap expects 'jQuery to be in a global space (Correct answer)
Bootstrap expects 'JQuery to be listed in the configuration
Bootstrap expects 'JQuery to be in a local space

Correct answer: Bootstrap expects 'jQuery to be in a global space

Many older JavaScript libraries, including Bootstrap, were designed to expect jQuery to be available as a global variable (e.g., `window.jQuery` or `window.$`). The line `S = jQuery = require("jquery");` ensures that jQuery is not only imported but also assigned to these global variables. This satisfies Bootstrap's dependency, allowing it to function correctly in environments where it expects global access to jQuery.

Question 7: Prepopulate a form in a React form component using which component lifecycle method

componentWillMount (Correct answer)
componentHasMounted
willTransitionFrom
willTransitionTo

Correct answer: componentWillMount

`componentWillMount` (now considered legacy and replaced by `constructor` or `getDerivedStateFromProps` in modern React) was a lifecycle method called just before a component mounts. It was a suitable place to set initial state based on props or other data, making it useful for prepopulating form fields before the component's initial render. For new code, `componentDidMount` for data fetching or `constructor` for initial state is preferred.

Question 8: What isn't a Browserify advantage?

Bundles Node files so they can be used in a browser
Increases HTTP requests to get JS modules (Correct answer)
Faster loading applications
None of the above

Correct answer: Increases HTTP requests to get JS modules

Browserify's primary advantage is that it allows developers to use Node.js-style `require()` statements in client-side JavaScript, bundling all dependencies into a single file. This process *reduces* the number of HTTP requests needed to load JavaScript modules, leading to faster loading applications, not increasing them. It streamlines module management for the browser by consolidating multiple files into one.

Question 9: Choose a programming language that isn't used in the ESLintrc file.

C (Correct answer)
JSON
JavaScript
YAML

Correct answer: C

The `.eslintrc` file is used to configure ESLint, a popular linter for JavaScript, to enforce coding standards and identify potential issues. These configuration files are typically written in formats like JSON, YAML, or JavaScript itself. C is a low-level compiled programming language and is not used for configuring JavaScript linters, as it operates at a different level of abstraction.

Question 10: What distinguishes the React Router?

Declaratively configure routes
Focused on the M in MVC
Simple nested approach
D)All of the above (Correct answer)

Correct answer: D)All of the above

React Router is a powerful library for declarative routing in React applications, allowing routes to be configured using JSX, which enhances readability and maintainability. It supports a simple nested approach for defining routes, enabling complex UI structures and dynamic navigation. Its focus is on managing the 'View' aspect of an application, providing a robust way to handle navigation and UI changes based on the URL.

Question 11: Which sentence allows a tag named 'InputComp' to use a React reusable text input component found in the file 'TextlnputComp.jsx'?

var InputComp = requestComponent('..l TextlnputComp.jsx');
var Input = require('../Text|nputComp.jsx');
var InputComp = require(‘../ TextlnputComp.jsx'); (Correct answer)
var InputComp = useComponent('../TextInputComp.jsx');

Correct answer: var InputComp = require(‘../ TextlnputComp.jsx');

In environments using CommonJS modules (like Node.js or when bundled with tools like Webpack/Browserify), the `require()` function is used to import modules from other files. This statement imports the component exported from `TextlnputComp.jsx` and assigns it to the variable `InputComp`, making it available for use within the current file as a React component.

Question 12: What is modified when an action is added to edit a component's data?

Dispatcherjsx, the application dispatcher config file
Index.jsx, the entry point of the application
ActionTypes.jsx, the actions keys file
Store.jsx, the component store (Correct answer)

Correct answer: Store.jsx, the component store

In the Flux architecture, actions describe what happened, but they don't directly modify data. Instead, actions are dispatched to the Dispatcher, which then sends them to relevant Stores. It is the Store's responsibility to listen for specific actions, update its own private state based on those actions, and then emit a change event. Therefore, when an action is added to edit data, the `Store.jsx` file (or the relevant store) is where the data modification logic resides.

Question 13: The rendering of JSX tiles needs

Browserify
Jquery
React
React-DOM (Correct answer)

Correct answer: React-DOM

JSX is a syntax extension that allows you to write HTML-like code within JavaScript, but browsers cannot directly interpret it. React-DOM is the library specifically designed to take your React components, including those defined with JSX, and efficiently render them into the actual browser's Document Object Model (DOM). It acts as the crucial bridge between your React application's virtual representation and what the user sees in the browser.

Question 14: Which React function will display child components of a given component?

displayComponent()
render() (Correct answer)
updateState()
renderComp()

Correct answer: render()

In React class components, the `render()` method is a fundamental and required lifecycle method. Its primary purpose is to return the JSX (or other valid React elements) that describes the user interface for that component, including any child components it contains. When React needs to display or update a component, it calls this method to determine what should be rendered on the screen.

Question 15: In React, which store function is not used to configure the change listener?

deregisterListener
registerListener
change
None of the above (Correct answer)

Correct answer: None of the above

This question refers to the Flux architecture, which is a pattern for managing application state. In Flux, stores typically provide methods like `addChangeListener` (or `registerListener`) and `removeChangeListener` (or `deregisterListener`) for components to subscribe to and unsubscribe from state changes. The term 'change' itself is an event or concept, not a store function used to configure listeners; therefore, none of the listed options are incorrect store functions for this purpose.

Question 16: What distinguishes the virtual DOM?

Optimized for dynamic Uis
JavaScript objects update faster (Correct answer)
DOM objects update fasterthan JavaScript Objects
None of the above

Correct answer: JavaScript objects update faster

The Virtual DOM is a lightweight, in-memory representation of the actual browser DOM, built using JavaScript objects. Manipulating these JavaScript objects is significantly faster and less resource-intensive than directly interacting with the browser's real DOM. React leverages this speed by first updating the Virtual DOM, then efficiently calculating the minimal changes needed before applying them to the slower, actual DOM.

Question 17: When added to a component's style, it determines the layout's primary axis, and when using React's flexbox, it determines the layout's primary axis.

flex
flexDirection (Correct answer)
Direction
None of the above

Correct answer: flexDirection

`flexDirection` is a core CSS property used in Flexbox layouts to define the main axis along which flex items are arranged. When applied to a component's style in React (especially in React Native or with inline styles), it determines whether children are laid out horizontally (`row`) or vertically (`column`). This property is essential for controlling the direction and flow of elements within a flexible container.

Question 18: In React, what is a Flux property?

Bidirectional
Framework
Pattern (Correct answer)
None of the above

Correct answer: Pattern

Flux is an application architecture or design pattern, not a framework or a library itself. It provides a set of principles for managing application state and data flow in a unidirectional manner, complementing React's component-based UI. While libraries like Redux implement Flux principles, Flux itself is the conceptual pattern that guides how data flows through an application.

Question 19: Which of the following packages best demonstrates React's utility?

Browsify
React-Router (Correct answer)
Jquery
Bootstrap

Correct answer: React-Router

React-Router is a widely used library that enables declarative routing in React applications, allowing for the creation of single-page applications with multiple views and navigation. It demonstrates React's utility by extending its capabilities beyond just UI rendering to include complex application structure and user experience. This package is a prime example of how React can be used to build full-featured web applications.

Question 20: What isn't a part of CommonJS that is used to specify modules?

Export module
Module declaration
Insert statement (Correct answer)
Require statement

Correct answer: Insert statement

CommonJS is a module specification primarily used in Node.js environments for organizing JavaScript code into reusable modules. Its core mechanisms involve `require()` for importing modules and `module.exports` (or `exports`) for defining what a module makes available. The concept of an 'insert statement' is not part of the standard CommonJS syntax for module definition or usage.

Question 21: Choose between JSX and JavaScript as a differentiating feature for use.

Viewing structure (Correct answer)
Keywords
Functions
Closing tags

Correct answer: Viewing structure

JSX (JavaScript XML) is a syntax extension that allows developers to write HTML-like code directly within JavaScript. Its primary differentiating feature is its ability to declaratively describe the viewing structure or user interface of a component, making it highly intuitive to visualize the rendered output. While JavaScript handles the logic, JSX focuses on defining the component's visual representation.

Question 22: In React, which of the following is also referred to as the Flux initialization action?

ItemStorejsx, the component storage
ActionTypesjsx, the actions keys file
Dispatcherjsx, the application dispatcher config file
Index.jsx, the entry point of the application (Correct answer)

Correct answer: Index.jsx, the entry point of the application

In many React applications, `index.jsx` (or `index.js`) serves as the main entry point where the entire application is bootstrapped and rendered into the DOM. This file often contains the initial setup for the application, including the first render of the root React component and potentially the initialization of the Flux architecture or dispatching initial actions. It is the starting point from which the application's lifecycle begins.

Question 23: Which post-installation characteristic of Flux is connected to data flow?

Two way binding
Three way binding
Unidirectional data flow (Correct answer)
Directional data flow

Correct answer: Unidirectional data flow

A fundamental characteristic of the Flux architecture is its strict unidirectional data flow. Data flows in a single, predictable direction: from actions, through a central dispatcher, to stores, and then to views (React components). This one-way flow makes application state changes easier to understand, debug, and manage, enhancing predictability and maintainability.

Question 24: Choose Gulp's primary competitor.

MGP
Grunt (Correct answer)
Bunch
Broccoli

Correct answer: Grunt

Gulp and Grunt are both popular JavaScript task runners designed to automate repetitive development tasks, such as compiling CSS preprocessors, minifying JavaScript, or running tests. They serve very similar purposes in a web development workflow, making Grunt Gulp's direct and primary competitor in the realm of build automation tools.

Question 25: Which React API function call will generate a React component?

React.createClass (Correct answer)
React.newComponent
React.newClass
React.createComponent

Correct answer: React.createClass

`React.createClass` was the original and historically standard way to create React components before the introduction of ES6 classes and, more recently, functional components with Hooks. It is a factory function that returns a component class, allowing developers to define component methods, state, and lifecycle hooks. While less common in modern React, it was the primary API for component creation for many years.

REACT Practice Test 1

Which of the following React functions will update the data of a component while remaining within the componentWillMount?