What JavaScript Experts Should Know

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When you think of your perfect JavaScript developer, what knowledge do you expect him to have besides understanding JavaScript? Here are a few ideas for you about what to expect from JavaScript coders’ knowledge base. What exact technologies should they be familiar with to contribute to your project productively? 

Do you need a mid, junior, or senior JS developer? What should senior JavaScript developers know? Here are a few ideas of what to look for when hiring a JavaScript programmer for your project. We’ll omit things like experience with version control, professional conduct, communication ability, or necessary coding skills.

Know the core of JavaScript

So what a JavaScript developer should know besides the company’s technology stack, style guide, and engineering philosophy is what you wouldn’t expect from a newbie in your company, but more of the pre-existing coding knowledge and standard libraries.

The developer should know how to code in JavaScript and be well familiar with the necessary language features, like:

  • Closure
  • Hoisting
  • Prototypes
  • Promises
  • Understanding of scope
  • Concurrency model as well as the event loop
  • JSON
  • Regular expression
  • ES6
  • Memory management 
What features should JavaScript experts know?

Also, read our article about the latest trends in JS-based game development.

JavaScript Closures

The closure is created when an inner function accesses its outer function variables and arguments. The internal function can access three scope chains: its variables, the external function’s variables and arguments, and global variables. For instance, an outer function has a variable a and returns the inner function, which utilizes this outer variable. Inner functions have access to their parent scope, even after the parent function has been executed.

Hoisting In JavaScript

Hoisting in JavaScript is a mechanism where function declarations and variables are placed at the top of their scope before code execution. With hoisting, regardless of where functions and variables are declared, they are moved to the top of their scope, no matter whether it is global or local. Remembering that there is no hoisting for the ES6 let and const variables is also important. In this particular case, there is a temporal dead zone for them.


When it comes to inheritance, JavaScript does not ensure class implementation. JavaScript works with prototype-based inheritance. It means that each object owns a separate property linked to another object called its prototype. The prototype object has its prototype, and so on, until an object reaches null as its prototype.

The ES6 classes in JavaScript are merely syntactic sugar around prototype-based inheritance. The prototypes might be confusing, but they provide a powerful mechanism for constructing objects in JavaScript.


A promise in JavaScript is an object that represents an eventual completion or failure of an asynchronous operation and its value. It might either be a resolved value or a reason it’s not resolved (for example, a network error). A promise can have three possible states, such as fulfilled, rejected, or pending. Promise users can attach callbacks to handle the fulfilled value or the reason for failure. A promise will start doing whatever task you give it as soon as the promise constructor is invoked.

The executor is the name of function passed to a new promise. After creating a new promise, the executor runs automatically and contains the producing code which should produce the result. JavaScript itself provides Its arguments, resolve and reject, are callbacks. When the executor gets the result, it should call one of these callbacks: resolve if it was successful or reject if there was an error.

Understanding Scopes

Scopes define the accessibility of variables, objects, and functions. In JavaScript, there are two types of scope: Local and Global. Variables declared within a function become Local to the function and can only be accessed from within it. A variable declared outside a function becomes Global and has a global scope. All scripts and functions can access a variable with a global scope.

Global variables are accessible and available for modification anywhere in the program, while access to local variables is available only inside the function declaration. Variables declared without a var keyword inside any function becomes global variables automatically.

Memory management

In any programming language, the memory life cycle allocates the memory you need, uses the allocated memory to read and write, and releases the allocated memory when it is not needed anymore. JavaScript automatically allocates memory after the declaration of variables Using values means reading and writing a variable or an object property in allocated memory.

The main memory management task is determining when the allocated memory is no longer needed. In JavaScript, automatic memory management, known as garbage collection, is used for this purpose. The garbage collector monitors memory allocation, defines when it is no longer needed, and claims it. 

The garbage collection algorithms rely on the concept of reference. This supposedly automatic resource freeing gives developers the false impression they can choose not to care about memory management. Global variables, forgotten timers, and closures are common root causes of memory leaks.

JavaScript expert coding

Know the whole ecosystem of software development

Besides these JavaScript development features, every JS coder must know the basics of web development. HTML and CSS expertise is vital for your developers to be able to perform complex tasks, including stylization and content support in various browsers and mobile devices

Managing JS frameworks

Depending on the project status and existing team, you may already have all technology stack chosen; otherwise, you may want to look for a Senior JS developer to build your project from scratch. 

Popular commercial JS frameworks and runtime environments JS experts should know

A senior JS developer has the utmost experience in coding, so they can choose the proper framework and other tools for your project. JavaScript experts must also know how to use the Node.js framework for API development, server-side rendering, and development of any real-time network applications. Knowledge of front-end architecture patterns is another competitive edge for any JS developer.

A middle JS programmer should be able to work effectively with the existing tools and frameworks on the project. If you decide to hire a junior coder, make sure that the candidate has experience working with your current tech stack. 

Every JavaScript expert should know how to work with the JS framework used in your project. Learn what the most popular JavaScript frameworks are and what they are used for in our dedicated article. Knowledge of React, one of the most popular frameworks nowadays, is a strong plus for any JavaScript developer. 

What Are JavaScript Developer Tools

It’s crucial to be able to debug issues that arise and understand how the systems work. JavaScript has a vast ecosystem of developer tools that enable coders to examine application code quality, perform QA analysis, and diagnose bugs. Usually, they come together with browsers.

Other Crucial Skills for a JS Programmer

What other JavaScript developer tools should your developer be familiar with: 

  • Debugging and testing frameworks
  • Task runners and module bundlers 
  • Tools for managing asynchronous code
  • Code linters and formatters
  • Tools for working with Networking and HTTP-based APIs
  • Package managers

Besides this, developers should know how to work with the browser API to be able to store data on the client, manipulate data, etc. Some projects may require visual representation with graphs or produce dynamic, interactive data visualizations, so your developers should have experience with such libraries as D3.js, Highcharts, and Chart.js.

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Building JS developers team

As a JavaScript development company, ELITEX has a perfect thought-out approach to selecting JS programmers for a customer’s project. The dedicated project manager and technical lead carefully study the application development needs and determine the required knowledge and skills to complete it. It allows us to determine the qualification of JavaScript coders required to perform the tasks. Our company has mostly middle and senior JS developers, so we find those who fit our needs.

Having this approach implemented, we select programmers and build a dedicated team to develop a mobile application or any custom software solution for our customers. Our works are tangible proof of our high standards in JavaScript development.

As technology is an ever-changing and continuously evolving programming language, our JS developers keep their hands on the pulse of the latest trends in JavaScript development. Are you looking to hire a JavaScript expert or a dedicated cross-functional development team, including UX designers, QA specialists, and software developers, for your project? Looking for a reliable IT outsourcing company? Consider contacting ELITEX, a leading JavaScript development company in Ukraine with over five years of extensive expertise.

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