It produces programs by composing mathematical functions and avoids shared state & mutable data.<ul><li>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.</li><li>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.</li></ul>

What is functional programming?

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

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

Good to hear:<ul><li>In situations where modules or functional programming don’t provide an obvious solution.</li><li>When you need to compose objects from multiple sources.</li><li>Any time you need inheritance.</li></ul>Red flags:<ul><li>No knowledge of when to use prototypes.</li><li>No awareness of mixins or `Object.assign()`.</li></ul>

When is prototypal inheritance an appropriate choice?

In JavaScript, prototypal inheritance is simpler & more flexible than class inheritance.<ul><li>Good to hear: Classes: create tight coupling or hierarchies/taxonomies; Prototypes: mentions of concatenative inheritance, prototype delegation, functional inheritance, object composition.</li><li>Red Flags: No preference for prototypal inheritance & composition over class inheritance.</li></ul>

What is the difference between classical inheritance and prototypal inheritance?

<ul><li>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.</li><li>Red flags: Unable to list disadvantages of one style or another.</li></ul>

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

Good to hear:  <ul><li>An understanding of what blocking means, and the performance implications. </li><li>An understanding of event handling, and why its important for UI code. </li></ul>

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

Good to hear:  <ul><li>Avoid class hierarchies. </li><li>Avoid brittle base class problem. </li><li>Avoid tight coupling. </li><li>Avoid rigid taxonomy. </li><li>Avoid the gorilla banana problem. </li><li>Make code more flexible. </li></ul>

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

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

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

The answer is never, or almost never. Certainly never more than one level.Good to hear:<ul><li>Rarely, almost never, or never.</li><li>A single level is sometimes OK, from a framework base-class such as <code>React.Component</code>.</li><li>“Favor object composition over class inheritance.”</li></ul>

When is classical inheritance an appropriate choice?

Good to hear:  <ul><li>React is the new Canonical example of one-way data flow. Cycle.js is another popular implementation of uni-directional data flow.</li><li>Angular is a popular framework which uses two-way binding. </li></ul>

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

“People, Process, Product”

In the years since I wrote this article, a lot has changed. When I wrote it, lots of developers were coming to JavaScript from languages like Java and C++, lacking any understanding of how objects…