10 Interview Questions Every JavaScript Developer Should Know - Deepstash
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814 reads

Can you name two programming paradigms important for JavaScript app developers?

JavaScript is a multi-paradigm language, supporting imperative/procedural programming along with OOP (Object-Oriented Programming) and functional programming. JavaScript supports OOP with prototypal inheritance.

  • Good to hear: Prototypal inheritance (also: prototypes, OLOO); Functional programming (also: closures, first class functions, lambdas).
  • Red flags: No clue what a paradigm is, no mention of prototypal oo or functional programming.


576 reads

What is functional programming?

It produces programs by composing mathematical functions and avoids shared state & mutable data.

  • Good to hear: Pure functions/function purity; Avoid side-effects; Simple function composition; Examples of functional languages: Lisp, ML, Haskell, Erlang, Clojure, Elm, F Sharp, OCaml, et.; Mention of features that support FP: first-class functions, higher-order functions, functions as arguments/values.
  • Red flags: No mention of pure functions / avoiding side-effects; Unable to provide examples of functional programming languages; Unable to identify the features of JavaScript that enable FP.


535 reads

What is the difference between classical inheritance and prototypal inheritance?

In JavaScript, prototypal inheritance is simpler & more flexible than class inheritance.

  • Good to hear: Classes: create tight coupling or hierarchies/taxonomies; Prototypes: mentions of concatenative inheritance, prototype delegation, functional inheritance, object composition.
  • Red Flags: No preference for prototypal inheritance & composition over class inheritance.


376 reads

What are the pros and cons of functional programming vs object-oriented programming?

  • Good to hear: Mentions of trouble with shared state, different things competing for the same resources, etc.; Awareness of FP’s capability to radically simplify many applications; Awareness of the differences in learning curves; Articulation of side-effects and how they impact program maintainability; Awareness that a highly functional codebase can have a steep learning curve; Awareness that a highly OOP codebase can be extremely resistant to change and very brittle compared to an equivalent FP codebase.
  • Red flags: Unable to list disadvantages of one style or another.


223 reads

When is classical inheritance an appropriate choice?

The answer is never, or almost never. Certainly never more than one level.

Good to hear:

  • Rarely, almost never, or never.
  • A single level is sometimes OK, from a framework base-class such as React.Component.
  • “Favor object composition over class inheritance.”


220 reads

When is prototypal inheritance an appropriate choice?

Good to hear:

  • In situations where modules or functional programming don’t provide an obvious solution.
  • When you need to compose objects from multiple sources.
  • Any time you need inheritance.

Red flags:

  • No knowledge of when to use prototypes.
  • No awareness of mixins or `Object.assign()`.


161 reads

What does “favor object composition over class inheritance” mean?

Good to hear:  

  • Avoid class hierarchies. 
  • Avoid brittle base class problem. 
  • Avoid tight coupling. 
  • Avoid rigid taxonomy. 
  • Avoid the gorilla banana problem. 
  • Make code more flexible. 


194 reads

What are two-way data binding and one-way data flow, and how are they different?

Good to hear:  

  • React is the new Canonical example of one-way data flow. Cycle.js is another popular implementation of uni-directional data flow.
  • Angular is a popular framework which uses two-way binding. 


182 reads

What are the pros and cons of monolithic vs microservice architectures?

Good to hear:  

  • Positive attitudes toward Microservices, despite higher initial cost vs Monolthic Apps. Despite higher initial cost, Microservices tend to perform and scale better.
  • Structure the App so that services are independent from each other. But easy to bundle together as a monolithic App in the beginning.


172 reads

What is asynchronous programming, and why is it important in JavaScript?

Good to hear:  

  • An understanding of what blocking means, and the performance implications. 
  • An understanding of event handling, and why its important for UI code. 


628 reads



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