Technologies Coding Problems Bookmarks Learning Paths

Technologies Coding Problems Bookmarks Learning Paths

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What is a first class function? | Functions | javascript Interview Questions | NextRound.in

Questions

7 of 18

1What is function overloading?

2What are pure functions?

3Explain the concept of a 'callback function' and provide an example of its usage.

4What are higher-order functions?

5What is the difference between an arrow function and a regular function?

6What are arrow functions and when would you use them?

7What is a first class function?

8What is class function?

9What is an immediately invoked function expression (IIFE)?

10What is the difference between a function declaration and a function expression?

11What is an anonymous function?

12What are function statements?

13What is typeof of a function?

14How do you define a function in JavaScript?

15What is a function in JavaScript?

16What is the constructor function?

17What is function expression?

18What is this length property of a function?

javascript

Event Loop and Runtime

Concurrency and Threading

Bytecode and Parsing

Execution Context

String Operations

Array Operations

Call Apply Bind

Iterator and Generator

Garbage Collector

Functional Programming

Higher Order Functions

07 / 18

What is a first class function?

Difficulty: 5/10

higher-order functions, closures, callbacks

1
A programming language is said to have First-class functions if functions in that language are treated like other variables.
2
So the functions can be assigned to any other variable or passed as an argument or can be returned by another function.
3
JavaScript treats function as a first-class citizen. This means that functions are simply a value and are just another type of object.

Scenario Questions

0-2 years experience

1We have an array of user objects and we need to format their names and filter out inactive ones. How would you pass formatting functions directly into '.map()' and '.filter()' instead of writing inline arrow functions every time?
2Imagine you're building a simple button click handler. You want to pass a function 'logClick' to 'addEventListener', but you need it to log a specific button ID. How would you write a function that returns another function to capture that ID?

Follow-up Questions

How does passing a function as a reference affect its execution context ('this')?
What is the relationship between first-class functions and closures in terms of memory management?
Can you explain the difference between a first-class function and a higher-order function?

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2-5 years experience

1We're refactoring a legacy codebase where we have a lot of repetitive API fetching logic. How would you design a higher-order function wrapper that takes a standard fetch function and automatically adds retry logic or logging to it?
2A developer on your team passed an object's method as a callback to a third-party event emitter, but when it executes, 'this.state' is undefined. What's happening under the hood with JavaScript's function handling here, and how would you fix it?

5-8 years experience

1In a React application, we're seeing performance degradation because handlers are being recreated on every render, breaking 'React.memo' downstream. How do you balance the use of inline closures versus stable function references, and how would you design a custom hook to solve this cleanly?
2We are building an Express-like middleware pipeline for a custom Node.js gateway. How would you design the composition engine that chains these middleware functions together, ensuring they execute sequentially and can halt the chain?

8+ years experience

1Our engineering org is debating migrating our core SDK from an object-oriented class-based architecture to a functional, composition-based approach using first-class functions. What are the long-term maintenance, bundle size, and API extensibility trade-offs of this architectural shift?
2We have a high-throughput Node.js microservice processing millions of events per minute. We've noticed a high garbage collection overhead traced back to short-lived closures and higher-order functions generated dynamically. How would you audit this and re-architect the hot paths to mitigate memory churn without sacrificing code readability?