700+ Front end Developer Interview Questions and Answers

The solution checks if an integer array can become non-decreasing by modifying at most one element.

• Iterate through the array and check if there are more than one decreasing pairs of elements.

• If there are more than one decreasing pairs, return false.

• If there is only one decreasing pair, check if modifying one of the elements can make the array non-decreasing.

• If modifying the element at index i-1 or i can make the array non-decreasing, return true.

• Otherwise, return false.

The task is to find the unique number in an array where all other numbers occur twice.

• The array size is given by N = 2M + 1, where M is the number of elements occurring twice.

• Loop through the array and use a hashmap to count the occurrences of each number.

• Return the number with a count of 1, as it is the unique number.

The question is about finding the shortest path distance from a source node to all vertices in an undirected graph.

• The graph is represented by the number of vertices and edges, followed by the edges and their distances.

• The task is to find the shortest path distance from the source node (0) to all other nodes.

• If a node is disconnected from the source node, print the maximum positive integer value (2147483647).

• Implement the function and return the shortest path distances in asc...read more

The task is to encode an N-ary tree into a binary tree and then decode the binary tree back into the original N-ary tree.

• Encode the N-ary tree by representing each node as a binary tree node with its first child as the left child and subsequent children as the right child.

• To decode the binary tree, traverse the binary tree and for each node, create a new N-ary tree node with its left child as the first child and subsequent right children as siblings.

• Use a level order traversa...read more

The task is to sort a singly linked list based on actual values instead of absolute values.

• Traverse the linked list and store the values in an array

• Sort the array using any sorting algorithm

• Create a new linked list using the sorted array

• Return the new linked list

The task is to check if there exists a path from a given source vertex to a destination vertex in a directed and unweighted graph.

• Read the number of test cases.

• For each test case, read the number of vertices and edges.

• Read the edges of the graph.

• Read the source and destination vertices.

• Implement a graph traversal algorithm (e.g., BFS or DFS) to check if a path exists from the source to the destination.

• Print 'true' if a path exists, otherwise print 'false'.

Use React Router's Redirect component to redirect to login page if user is not logged in.

• Create a PrivateRoute component that checks if user is logged in

• If user is not logged in, redirect to login page using Redirect component

• Wrap the routes that require authentication with PrivateRoute component

The diameter of a binary tree is the length of the longest path between any two end nodes in the tree.

• The diameter of a binary tree can be calculated by finding the maximum of the following three values: 1) the diameter of the left subtree, 2) the diameter of the right subtree, and 3) the longest path that passes through the root node.

• To find the diameter of a binary tree, we can use a recursive approach. We calculate the height of the left and right subtrees, and then calcul...read more

Use the accept attribute in the input tag to only allow jpg and png files.

• Add accept attribute to input tag with 'image/jpeg, image/png' value

• This will restrict file selection to only jpg and png files

Use flexbox to center align a div in just one line in CSS.

• Set the parent container's display property to flex.

• Use the justify-content property with the value 'center' to horizontally center the div.

• Use the align-items property with the value 'center' to vertically center the div.

Javascript is single-threaded.

• Javascript runs on a single thread called the event loop.

• This means that it can only execute one task at a time.

• However, it can delegate tasks to other threads using web workers.

• This allows for parallel processing without blocking the main thread.

Implement a calculator class with chaining methods and delay function.

• Create a Calculator class with add, sub, mul methods that return the instance of the class.

• Implement a delay method that uses setTimeout and returns the instance of the class.

• Use a queue to store the operations and execute them in order after the delay.

• Return the result of the operations when the equals method is called.

Remove duplicate elements from an Array

• Use the Set object to remove duplicate elements

• Convert the Set back to an array using the spread operator

• If the array contains objects, use a custom comparison function

CSS media queries are used to apply different styles based on device characteristics. Min and max define the range of values.

• Media queries allow for responsive design by adapting to different screen sizes and orientations

• Min-width and max-width are commonly used to define the range of screen sizes

• Min-device-width and max-device-width are used to target specific device characteristics

• Other media query features include min-height, max-height, orientation, and resolution

JavaScript is considered a dynamic language because variables can change types based on their current value.

• Variables in JavaScript can hold different types of values at different times

• The type of a variable is determined at runtime, not at compile time

• Dynamic typing allows for flexibility and ease of use in JavaScript programming

• Example: a variable can start as a number and then be reassigned as a string

Functional components and class components are not the same in React. Functional components are simpler and more lightweight, while class components have additional features like state and lifecycle methods.

• Functional components are stateless and are just JavaScript functions that return JSX.

• Class components have access to state and lifecycle methods like componentDidMount and componentDidUpdate.

• Functional components are easier to read and test, while class components can be ...read more

Debounce the API call on input change to optimize performance.

• Implement a debounce function to delay the API call until the user has finished typing.

• Set a time interval for the debounce function to wait before making the API call.

• Cancel the previous API call if a new input change occurs before the time interval is up.

• Use a loading spinner to indicate to the user that the API call is in progress.

• Consider using a caching mechanism to store the API response for future use.

jQuery is a fast, small, and feature-rich JavaScript library.

• jQuery simplifies HTML document traversing, event handling, and animating.

• It provides a set of methods for AJAX interactions and DOM manipulation.

• jQuery is cross-platform and supports a wide range of browsers.

• It has a large community and a vast number of plugins available.

• Project architecture depends on the specific project and its requirements.

Develop an app to show all airports in a country on a map and allow users to report incidents after logging in.

• Use a map API like Google Maps or Mapbox to display all airports in the country

• Implement a login system for users to report incidents

• Create a form for users to report incidents with fields like airport name, incident type, and description

• Store incident reports in a database for future reference and analysis