40+ Javascript Developer Interview Questions and Answers

Promise in JS is an object representing the eventual completion or failure of an asynchronous operation.

• Promises are used to handle asynchronous operations in JavaScript.

• They can be in one of three states: pending, fulfilled, or rejected.

• Promises can be chained using .then() method to handle success and failure cases.

• Example: new Promise((resolve, reject) => { ... }).then(result => { ... }).catch(error => { ... });

JavaScript state handling globally involves managing application state across components using various techniques.

• Global variables: Use global variables to store state, but be cautious of potential conflicts.

• Singleton pattern: Create a single instance of a state management object to share state across components.

• Event Emitters: Use event-driven architecture to handle state changes and notify components.

• State management libraries: Utilize libraries like Redux or MobX for struc...read more

Types of operators include arithmetic, assignment, comparison, logical, bitwise, and more.

• Arithmetic operators perform mathematical operations (+, -, *, /, %)

• Assignment operators assign values to variables (=, +=, -=, *=, /=)

• Comparison operators compare values (==, !=, >, <, >=, <=)

• Logical operators combine multiple conditions (&&, ||, !)

• Bitwise operators manipulate individual bits (&, |, ^, ~, <<, >>)

• Unary operators operate on a single operand (++, --)

Async await is a feature in JavaScript that allows for asynchronous code to be written in a synchronous manner.

• Async await is built on top of promises and provides a cleaner syntax for handling asynchronous operations.

• It allows you to write asynchronous code that looks like synchronous code, making it easier to read and maintain.

• The 'async' keyword is used to define a function as asynchronous, while the 'await' keyword is used to pause the execution of the function until a pr...read more

Call stack is a data structure that stores information about the active subroutines of a computer program.

• Call stack is a LIFO (Last In, First Out) data structure.

• It keeps track of function calls in a program.

• When a function is called, it is added to the top of the call stack. When it returns, it is removed.

The event loop is a mechanism in JavaScript that allows for asynchronous operations to be executed in a non-blocking manner.

• The event loop continuously checks the call stack for any functions that need to be executed.

• If the call stack is empty, the event loop checks the task queue for any pending tasks.

• The event loop prioritizes tasks in the microtask queue over the macrotask queue.

JavaScript scope defines the accessibility of variables, while block scope restricts variable visibility to specific code blocks.

• Scope determines where variables can be accessed in the code.

• Global scope: Variables declared outside any function are accessible everywhere.

• Function scope: Variables declared within a function are only accessible inside that function.

• Block scope: Introduced with 'let' and 'const', variables declared within a block (e.g., if statements) are not acce...read more

let is block scoped, var is function scoped, const is block scoped and cannot be reassigned.

• let: block scoped variable declaration

• var: function scoped variable declaration

• const: block scoped constant declaration, cannot be reassigned

I have extensive experience with CI/CD pipelines, automating testing and deployment processes for JavaScript applications.

• Implemented CI/CD using Jenkins for automated builds and deployments.

• Utilized GitHub Actions to run tests and deploy to production on every commit.

• Configured Docker containers for consistent environments across development and production.

• Integrated automated testing frameworks like Jest and Cypress in the CI pipeline.

• Monitored deployments with tools like N...read more