Interview questions · Part 1
Top 50 JavaScript Interview Questions with Answers (Free PDF)
By Gaurav SharmaPublished
49 pages covering the 50 most-asked JavaScript interview questions, each with a short answer to say first and a detailed explanation: var/let/const, hoisting, closures, this, the event loop and output puzzles, promises and async/await, plus coding answers for debounce, throttle, deep clone, Promise.all, bind, curry, memoize and an LRU cache, with Hinglish explanations.
- Pages
- 49
- Format
- A4 PDF
- Language
- English + Hinglish
- Price
- Free by email
What's inside
Preview: 5 of 50 JavaScript interview questions
Read a sample of the questions and answers here. Email me for the complete PDF with detailed explanations, code, outputs, traps and follow-up questions.
01What is the difference between var, let and const?
varis function-scoped, hoisted with the valueundefinedand can be redeclared.letandconstare block-scoped and stay in the Temporal Dead Zone until their line runs.constalso can't be reassigned.EasyMost asked
02What are the data types in JavaScript?
8 types: 7 primitives (string, number, bigint, boolean, undefined, null, symbol) and object. Arrays, functions and dates are all objects. Primitives are immutable and copied by value; objects are shared by reference.
Easy
03What is the difference between == and ===?
===(strict) compares value and type with no conversion.==(loose) first converts the types (coercion), then compares. Always use===; the one accepted exception isx == null, which checks null or undefined.EasyMost asked
04What is the difference between null and undefined?
undefinedmeans a value was never assigned (JavaScript sets it).nullis an intentional "no value" that the programmer sets.Easy
05What is hoisting? Predict the output.
Before running, JS registers every declaration: functions fully,
varasundefined,let/const/classuninitialised (TDZ).EasyMost asked
These are the 50 JavaScript questions that come up again and again in fresher and junior interviews, in the order of difficulty you're likely to face them. Every answer starts with a short version you can say in two lines, then explains the why with code, output and the traps interviewers look for.
What does each answer include?
- A short answer first. The one or two lines to say before going into detail, so you never ramble.
- A detailed explanation. Code you can paste into the console, the exact output, and tables or sketches for things like the event loop and the prototype chain.
- Traps and follow-ups. The mistakes people make and the next question the interviewer usually asks.
- Coding answers. Working implementations of debounce, throttle, deep clone, flatten, Promise.all, bind/call/apply, curry, memoize, an EventEmitter, retry with backoff and an LRU cache.
How should you prepare with these questions?
Start with the starred "most asked" questions in the index. Read each short answer out loud, run the snippets yourself, and write the 8 coding questions from memory at least once. The night before, revise from the two pages of one-line answers at the end.
This is Part 1 of the Interview Q&A series. To learn the concepts behind these answers, start with the free JavaScript handwritten notes.
FAQ
Questions about this PDF
Is this JavaScript interview questions PDF free?
Yes. The full 49-page PDF with all 50 questions and answers is free; email me to request the complete PDF.
Are these JavaScript questions good for freshers?
Yes. Questions 1 to 15 cover fresher basics like var/let/const, hoisting, closures and this. Questions 16 to 35 cover async JavaScript and the DOM, and 36 to 50 are the coding and polyfill questions asked for 0 to 2 years of experience.
Does the PDF include output-based questions?
Yes. It includes the common predict-the-output questions on hoisting, == coercion, closures in loops, this, microtasks vs macrotasks and async/await ordering, each with a step-by-step explanation.
How is this different from the JavaScript handwritten notes?
The handwritten notes (Placement Series, Part 1) teach the concepts one page at a time. This PDF is the interview layer on top: the exact questions, a short answer to say first, the detailed answer, traps and follow-up questions.
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