TOP 5 JAVASCRIPT DEVELOPER INTERVIEW QUESTIONS YOU HAVE EXPERIENCED
JavaScript is a special language that plays a significant role in most large-scale applications. What defines the essence of JavaScript and sets it apart from other languages?
Interviewing for a JavaScript Developer position is a challenging process that requires candidates to have a deep understanding of this programming language down to every detail. Here are the TOP 5 interview questions that almost every JavaScript Developer has to go through.
1. Please name two important programming paradigms for JavaScript Developers?
JavaScript is a multi-paradigm language that supports both imperative/procedural programming along with Object-Oriented Programming (OOP) and functional programming. JavaScript supports OOP with prototypal inheritance.
In the answer, include:
- Prototypal inheritance (or: prototypes, OLOO).
- Functional programming (or: closures, first-class functions, lambdas). Red flags:
- Lack of understanding of what a paradigm is, failure to mention prototypal OO or functional programming.
2. What is the difference between classical inheritance and prototypal inheritance?
Class Inheritance: It allows you to build a new class based on the definitions of an existing class. This means that a parent class can share data and methods with child classes. Instances are often initialized through constructor functions using the "new" keyword. Class inheritance may or may not use the "class" keyword introduced in ES6.
Prototypal Inheritance: Prototype is a mechanism through which objects in JavaScript inherit features from another object. It is typically accomplished using the "Object.create()" method. Instances can be created from various different objects, allowing for selective and flexible inheritance.
In JavaScript, prototypal inheritance, which involves inheriting directly from prototypes, is simpler and more flexible compared to classical inheritance, which involves class-based inheritance.
The answer should include:
- Classes: Creating tightly coupled or hierarchical classes.
- Prototype: Referring to prototype-based inheritance, delegation, functional inheritance, object composition.
Red flags:
- No preference for prototypal inheritance and object composition over class inheritance.
3. What is Functional Programming?
Functional programming is a programming paradigm that constructs programs by composing mathematical functions and avoids shared state and mutable data. Lisp was one of the earliest languages to support functional programming and drew significant inspiration from lambda calculus. Lisp and many Lisp-like languages are still widely used today.
Functional programming is a fundamental concept in JavaScript (one of its two pillars). Some common functional utilities have been added to JavaScript in ES5.
The answer should include:
- Pure functions
- Avoiding side-effects
- Simple functional components
- Examples of functional languages: Lisp, ML, Haskell, Erlang, Clojure, Elm, F Sharp, OCaml, etc.
- Mention features supporting functional programming in JavaScript: first-class functions, higher-order functions, functions as arguments/values.
Red flags:
- Failure to mention pure functions and avoiding side-effects in JavaScript.
- Inability to provide examples of functional programming languages.
- Inability to identify which features of JavaScript enable functional programming.
4. Advantages and Disadvantages of Functional Programming and Object-Oriented Programming?
Advantages of OOP:
- Easy to understand the basic concept of objects and the meaning of method calls.
- Tends to use imperative style more than declarative style, which is like a set of step-by-step instructions for the computer to follow.
Disadvantages of OOP:
- Often relies on shared state. Objects and behaviors are often tightly coupled on the same entity, accessible by any number of functions with an unpredictable order, potentially leading to unintended behavior like race conditions.
Advantages of FP:
- Uses a functional model, allowing developers to avoid shared state and side effects, helping eliminate errors caused by multiple functions competing for the same resource.
- With features like point-free style (also known as tacit programming), functions tend to be simplified and easily rearranged for more frequent code reuse compared to OOP.
- FP tends to support declarative and expressive styles, focusing on what needs to be done (what) and letting basic functions handle how it's done.
Disadvantages of FP:
- Overexploiting FP features like point-free style and large compositions can reduce readability because the resulting code is often more abstract, concise, and less specific.
- Many people are more familiar with OOP and imperative programming than FP, so even common terminology in FP can be confusing to newcomers.
- FP has a steeper learning curve compared to OOP due to the widespread popularity of OOP, which has created a vibrant community and documentation around OOP languages. FP languages tend to be more academic and formal, often requiring a prior knowledge foundation in areas like lambda calculus, algebra, and category theory to fully grasp FP concepts.
In the answer, you should:
- Mention the issues with shared state, competition for the same resource, etc.
- Highlight FP's ability to greatly simplify many applications.
- Address differences in learning curves.
- Analyze side effects and their impact on program maintainability.
Red flags:
- Inability to list disadvantages of both programming styles because anyone with experience in either style will have faced some limitations.
5. Two-way data binding and one-way data flow in JavaScript are two different approaches to handling data interactions in an application?
Two-way data binding means that user interface (UI) elements are bound to dynamic model data so that when a UI element changes, the model data changes accordingly, and vice versa.
One-way data flow means that the model is the single source of truth. Changes in the UI trigger notifications indicating the user's intent to the model (or "store" in React). Only the model has the authority to modify the application's state. As a result, data always flows in a single direction, making it more predictable and understandable.
One-way data flow is deterministic, while two-way data binding can lead to harder-to-track and capture side effects.
Key points to include in the answer:
- React is a modern and classic example of one-way data flow, so mentioning React is a good signal.
- Cycle.js is another popular implementation of one-way data flow.
- Angular is a common framework that uses two-way data binding.
Red flags:
- Lack of knowledge about these concepts or an inability to explain the differences.
In this response, Jung Talents has explored the TOP 5 common interview questions for JavaScript Developers. Understanding and preparing for these questions not only boosts your confidence during interviews but also increases your chances of getting hired. Good luck!
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