Promilo Reactjs Developer Interview Questions and Answers

Create a timer component in React for tracking time.

• Use state to store the current time

• Use setInterval to update the time every second

• Display the time in a user-friendly format

Fetch API calls are executed in the browser's JavaScript environment.

• Fetch API calls are executed asynchronously in the browser's event loop.

• They are typically triggered by JavaScript code in response to user actions or other events.

• The fetch API call is made from the client-side JavaScript code and sent to the server to retrieve data.

• Once the data is received, the fetch API call processes the response and updates the

Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope.

• Hoisting applies to both variable and function declarations.

• Variable declarations are hoisted but not their initializations.

• Function declarations are fully hoisted, allowing them to be called before they are declared.

• Hoisting does not apply to variables declared with let or const.

• Hoisting can lead t...read more

Higher-order functions are functions that take one or more functions as arguments or return a function as their result.

• Higher-order functions can be used to create reusable code by abstracting common patterns.

• They enable functional programming paradigms like currying and composition.

• Examples of higher-order functions in JavaScript include map, filter, and reduce.

var is function scoped, let and const are block scoped.

• var can be redeclared and updated within its scope

• let can be updated but not redeclared within its scope

• const cannot be updated or redeclared once declared

• let and const are not hoisted like var

• const must be initialized during declaration

Hooks are a feature in React.js that allow developers to use state and other React features in functional components.

• Hooks are functions that let you use React features in functional components

• They allow you to use state and other React features without writing a class

• Hooks provide a way to reuse stateful logic between components

• Some commonly used hooks are useState, useEffect, and useContext

Var is function scoped, let is block scoped. Redux is a predictable state container, Flux is an architecture pattern.

• Var can be redeclared and updated within its scope, let cannot be redeclared but can be updated within its scope

• Redux has a single store for the entire application, while Flux has multiple stores

• Redux uses a unidirectional data flow, while Flux uses a bidirectional data flow

• Redux has middleware for handl...read more

Conditional rendering in React allows components to render different elements or components based on certain conditions.

• Conditional rendering is achieved using JavaScript expressions inside JSX.

• Common conditional rendering techniques include using if statements, ternary operators, and logical && operator.

• Example: rendering a component only if a certain condition is met - {condition ? : null}

DOM tree is a hierarchical representation of HTML elements in a web page.

• DOM stands for Document Object Model.

• It is a tree-like structure where each node represents an HTML element.

• The DOM tree is created by the browser when a web page is loaded.

• It allows JavaScript to manipulate the content, structure, and style of a web page.

Props are immutable and passed from parent component, while state is mutable and managed within the component.

• Props are read-only and cannot be modified by the component receiving them.

• State is mutable and can be changed by the component that owns it.

• Props are passed from parent to child components, while state is managed within the component itself.

• Example: Props can be used to pass data from a parent component to a c...read more

Redux is a predictable state container for JavaScript apps. It is used to manage application state in a centralized way.

• Use Redux when you have complex state management needs in your application.

• Redux is helpful for large applications with many components that need access to the same state.

• Avoid using Redux for simple applications with minimal state management requirements.

• Consider using React's built-in state manageme...read more

Remove elements from source array present in another array passed to a function

• Loop through elements in source array and check if they exist in the other array

• If an element is found in both arrays, remove it from the source array

DOM tree is a hierarchical representation of HTML elements in a web page.

• DOM stands for Document Object Model

• It is a tree-like structure where each node represents an HTML element

• The root node is the element, followed by and elements

• Nodes can have parent-child relationships, siblings, and descendants

• JavaScript can manipulate the DOM to dynamically update the content and structure of a web page