500+ Javascript Interview Questions with Answers 2026

JavaScript Fundamentals (15%): Compilation phase mechanics like variable and function hoisting, the dynamic execution context of the this keyword, prototype chain linking, prototypal inheritance, and execution context tracking.

Asynchronous Programming (18%): Managing event-driven runtimes using Promises, orchestrating non-blocking workflows with async/await, resolving callback hell, macro/microtask queue sequencing, and error handling inside async iterations.

Web APIs and DOM Manipulation (12%): Fetching network resources using the Fetch API, structural DOM events and propagation mechanics (bubbling vs. capturing), complex element manipulation, CSS selector querying, and node traversal patterns.

JavaScript Frameworks and Libraries (10%): Foundational architectural concepts behind major web layers (React, Angular, Vue.js), predictable state management paradigms, lifecycle execution, and modular component boundaries.

Error Handling and Debugging (8%): Catching runtime exceptions using try-catch blocks, analyzing native error types (TypeError, ReferenceError, SyntaxError), leveraging browser developer tools, deep console monitoring, and predictable resilience strategies.

Advanced JavaScript Topics (12%): Coroutine mechanics with generators, custom iterable design via iterators, meta-programming constructs using Symbols, object interception with Proxies, and reflective operations through the Reflect API.

Code Quality and Best Practices (5%): Structural design patterns, scalable naming conventions, semantic code readability improvements, front-end unit testing paradigms, and peer code review standards.

B) Start, End, Timeout, Promise 1, Promise 2

C) Start, End, Promise 1, Promise 2, Timeout

D) Start, Promise 1, End, Promise 2, Timeout

E) Start, End, Promise 1, Timeout, Promise 2

F) Start, Timeout, End, Promise 1, Promise 2

Why it is correct: The JavaScript engine processes synchronous tasks first, meaning "Start" and "End" print immediately. When synchronous code finishes executing, the event loop prioritizes the Microtask Queue over the Macrotask Queue. Promise callbacks go directly into the Microtask Queue and execute completely before the loop processes any scheduled setTimeout callbacks from the Macrotask Queue.

Why alternative options are incorrect:

Option B is incorrect: This option places the macrotask setTimeout ahead of microtasks, which violates event loop prioritization rules.

Option D is incorrect: This option assumes the first Promise callback runs before the synchronous console statement at the bottom of the script.

Option E is incorrect: This option incorrectly breaks up the Promise microtask chain to execute a waiting macrotask.

Option F is incorrect: This sequence treats setTimeout as a synchronous execution block rather than a queued asynchronous task.

B) 3, 3, 3

C) 2, 2, 2

D) 0, 0, 0

E) undefined, undefined, undefined

F) The program throws a ReferenceError before printing anything.

Why it is correct: Variables declared with the var keyword are functionally or globally scoped, meaning they are not bound to the block scope of a loop. A single variable instance i is shared across every loop iteration. By the time the asynchronous setTimeout callbacks execute 100 milliseconds later, the synchronous loop has already finished running, leaving the final value of i at 3.

Why alternative options are incorrect:

Option C is incorrect: The loop breaks only when the condition evaluates to false, which occurs when i reaches 3, not 2.

Option D is incorrect: The shared counter variable continues incrementing, so it does not freeze at its initial loop state.

Option E is incorrect: The variable remains accessible throughout the scope chain and retains its final numeric value of 3.

Option F is incorrect: The syntax and identifiers are completely valid, which avoids throwing a compile-time or runtime exception.

B) Alex, undefined

C) undefined, Alex

D) undefined, undefined

E) The execution throws a TypeError on the arrow function call.

F) The execution throws a SyntaxError during object definition.

Why it is correct: The execution context of a standard function depends entirely on how you call it. Extracting user.greet and calling it as unboundGreet() separates it from its parent object, binding this to the global window object where name is undefined. For user.farewell, arrow functions do not have their own this binding context. Instead, they look up the lexical scope chain to inherit this from the surrounding context, which points to the global object where name is also undefined.

Why alternative options are incorrect:

Option B is incorrect: The standalone function reference unboundGreet() loses its object binding context upon assignment.

Option C is incorrect: This option mistakenly treats standard function references as lexically bound and arrow functions as dynamically bound.

Option E is incorrect: Arrow functions are perfectly valid object properties; invoking them returns a value instead of crashing.

Option F is incorrect: Object definitions can safely hold both standard and arrow functions without triggering compiler issues.

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