JavaScript Interview Questions: Introduction
An introduction to common JavaScript interview questions asked by top software engineering companies.
JavaScript Interview Questions: Introduction
JavaScript interview questions are asked by almost every top software engineering company. Here is an introduction to what to expect and how to prepare.
What This Series Covers
- call, apply, and bind: function invocation and
thiskeyword manipulation. - Polyfill for bind: implementing bind from scratch.
- Currying: transforming multi-argument functions into chained single-argument functions.
- Debouncing: optimizing event handling by controlling function execution frequency.
- async and defer: script loading strategies for optimized rendering.
- Event bubbling: DOM event propagation mechanism.
- Event delegation: efficient event handling with a single listener.
- Sum(1)(2)(3)(4)..(n): curried function chaining (Amazon question).
- Prototypes and prototypal inheritance: JS inheritance model.
- Recursion: solving problems with recursive functions.
- CORS and preflight requests: cross-origin resource sharing.
- Debouncing vs Throttling: when to use each (Walmart question).
- Throttling: limiting function execution rate (Walmart question).
How to Prepare
- Understand the concept: read and understand each topic deeply.
- Implement from scratch: write polyfills and implementations without libraries.
- Practice coding: solve the questions on paper or in an editor.
- Explain clearly: practice explaining the concept in simple terms.
- Know the use cases: understand when and why to use each technique.
What Companies Ask
- Amazon: sum(1)(2)(3)(4)..(n) (currying).
- Flipkart: debouncing.
- Walmart: throttling, debouncing vs throttling.
- Ola: async and defer attributes.
- Oyo: event bubbling.
- All companies: call/apply/bind, polyfills, closures, promises, prototypes.
The Takeaway
JS interview questions cover: call/apply/bind, polyfills, currying, debouncing, throttling, async/defer, event bubbling, event delegation, prototypes, recursion, and CORS. Prepare by understanding each concept, implementing from scratch, practicing coding, and knowing the use cases. Top companies ask these questions regularly.
call/apply/bind, polyfills (bind, map, filter, reduce), currying, debouncing, throttling, async/defer, event bubbling, event delegation, prototypes, recursion, CORS, and closures. Amazon asks currying, Flipkart asks debounce, Walmart asks throttle, Ola asks async/defer, Oyo asks event bubbling.
Understand each concept deeply, implement polyfills and utilities from scratch (no libraries), practice coding in an editor, practice explaining in simple terms, and know the real-world use cases for each technique.
sum(1)(2)(3)(4)..(n) - a currying question where you implement a function that can be chained to sum numbers. This tests understanding of currying, closures, and function chaining.
Debouncing - implementing a debounce function that delays the execution of a function until the user stops calling it for a specified delay. This tests understanding of closures, setTimeout, and event optimization.
Throttling and the difference between debouncing and throttling. Implementing a throttle function that limits the rate of function execution. This tests understanding of closures, timestamps, and event optimization.
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