Hire senior and proven JavaScript developers

Before starting this process, you need a precise (but customizable) job ad to attract only the best JavaScript developers. And you should follow a roadmap for every recruitment stage.

About JavaScript

JavaScript is a lightweight, object-oriented, dynamic scripting language for creating web apps, web browser interactive effects, game development, mobile apps, backend infrastructures, and more.

It was previously known as LiveScript and released in 1995.

Despite being famous for web page use, JavaScript is also used in non-browser environments, and its syntax is similar to that of C++ and Java.

Sourcing and interviewing a JavaScript Developer

When hiring the best JavaScript developer, you should use well-researched recruitment strategies beforehand.

Some steps aren't only preferable but essential. Here are a few.

Technical skills checklist

An experienced JavaScript developer will have excellent knowledge in some (or ideally all) of the following:

• JavaScript basics, ES6+, HTML and CSS, DOM

• JavaScript concepts (Loops, Variables, and Functions)

• Basic algorithms and data structures

• Common JavaScript frameworks and libraries (e.g., jQuery, TypeScript, Angular, Vue.js, or React.js)

• JavaScript state management tools (e.g., Redux.js)

• Web development tools (NPM, Git, or Webpack)

• Following the best practices of JavaScript and its features

• Collaborating closely with the frontend developers and UX/UI designers

• Analyzing system risks and requirements

• Asynchronous programming (Prototypes, Hosting, Scope, Coercion, etc.)

We also discuss the ins and outs with Diamant Isufi, a Software Engineer at Proxify, to describe more about what else the JavaScript developer must know:

"In addition to possessing adept problem-solving acumen, a developer should demonstrate a profound mastery of fundamental JavaScript concepts, as they are the most important thing when getting started. This allows you to understand JavaScript's underlying mechanisms, applications, and rationale for implementation. A developer should be able to learn elemental data types, variables, functions, classes, OOP concepts, and also the modularity that JavaScript works with."

Checklist of preferred qualifications

To find those diamonds in the rough in hundreds of candidates, you can shortlist the ones who also have:

• A degree in Computer Science or a related field

• Solid knowledge of JavaScript platforms (e.g., Meteor)

• Knowledge of ES6 language features (e.g., ECMAScript 6)

Interview questions and answers

Use the following questions and their example answers when you assess JavaScript developer candidates.

1. Can you define isNaN and its usage?

Example answer: NaN means "not a number," and isNaN lets us know which value is, in fact, NaN. When we use the function isNaN(), we try to discover if a value has an incorrect or illegal number. If this function returns as 'true' the examined value is NaN.

2. Can you define "negative infinity"?

Example answer: If we divide a negative number by zero, we get a negative infinity number in JavaScript. This number is a constant value, the lowest we can receive, and there is no lower value than this.

3. Could you explain the "global variables "?

Example answer: Global variables can be accessed from anywhere in the program. Global variables are always declared via a window object or outside a function. We can access them from any other function. An example of a global variable is var.

4. Can you differentiate between SessionState and ViewState in JavaScript?

Example answer: The SessionState is data that persists in a specific server. When we close the browser, or a session expires, this data availability also stops. We can access this precise data from all web app pages.

The ViewState is a group of controls' values on a page and the client browser. ViewState stores information only on the client's side.

The SessionState is saved on a server, but the ViewState is saved on the page itself, and we can see it from just a single page, not more.

5. Can you define the "looping structures" in JavaScript?

Example answer: We use these looping structures when we work on repetitive tasks, i.e., this feature helps us to repeat functions. The loops don't stop running unless their condition appears "false.”

There are seven looping structures in JavaScript:

• for…in
• for…of
• do-while
• while
• for
• forEach()
• map()

6. Define "null" in JavaScript?

Example answer: "null' means either no object or no value. The other name for this is null string, which intentionally has no value. We call this a primitive value because it has no array object.

For context, the primitive values can be divided into:

• Number
• Boolean
• String
• Null
• Undefined

7. Can you explain how to use 'Void(0)'?

Example answer: 'Void' in JavaScript represents 'return of nothing,' an empty value. So, when we use 'Void(0), we call a different method without refreshing the page. Further, when we use "javascript:void(0)," we always do this in an anchor tag, and this prevents reloading of the page. Also, we can call the JavaScript functions on a single or double click this way.

8. Can you explain more about the 'pop()' method?

Example answer: We use this method when we need to remove the last array element, i.e., pop() helps us retrieve that same element once someone removes it. This way, we adjust the array length accordingly with the help of the syntax array.pop()

9. Can you differentiate between .call() and .apply()?

Example answer: These two are similar to one another. If we know some function's arguments and the function number, we use .call() as a predefined method. With this method, a specific object can take on another method from a different object.

On the other hand, we use .apply() if we don't know the function number, but we can write a method we can later use on more different objects.

10. Can you elaborate on the deferred scripts in JavaScript?

Example answer: Defer in JavaScript refers to a boolean attribute and its role in determining when a downloaded script is synched to the page parsing. The script must be executed only after parsing is complete.

The deferred scripts in JavaScript postpone script execution when the HTML page parser is active. The result of this is shorter web page loading time and quicker displaying.

11. What are arrow functions in JavaScript?

Example answer: We use these functions to create anonymous expressions or write expressions for anonymous functions. Such functions don't support the keywords new target, arguments, super, or this.

We use arrow functions when passing a function like a parameter for another demanding function.

12. What are the JavaScript data types?

Example answer: There are six such types, divided into three categories:

• Primary (primitive) – Boolean, String, and Number
• Composite (or reference) – Object, Function, and Array
• Special – Null and Undefined data type

13. Can you compare undefined and non-defined variables?

Example answer: Both variable types here are linked to memory space. The undefined variable exists in memory space but without a value assigned to it.

The non-defined variable is non-existent in the memory space but is referenced elsewhere.

14. Can you describe the JavaScript timers?

Example answer: We use timers to execute a specific function or task within a timeframe. They help us delay a program execution or code and help us execute the code on time. All timers operate in one thread, and subsequent events queue up afterward.

15. What is automatic type conversion?

Example answer: This is a process of assigning values. We assign a specific value from one numeric data type to another. In JavaScript, this automatic type conversion is frequently enabled and supported.

16. What is event delegation?

Example answer: With the JavaScript delegation model, we organize the event handling better. If we want to use just one handler for several elements simultaneously, we first conduct a 'bubble' and then capture the handler to apply it to more parts simultaneously.

This is called event delegation.

17. Can you define JavaScript cookies?

Example answer: When a user visits a website, the website will always store some tiny test files in the computer, which we call cookies. They automatically get created during user visits, but only when the user inserts some of their information into certain forms/subscriptions (e.g., shopping cart checkout or filling out forms).

The website always asks the user for permission to do this.

18. Why would you wrap the whole JavaScript source file content in a function block?

Example answer: This is a widespread practice JavaScript developers who rely on JavaScript libraries for it (Node.js or jQuery most frequently). With this, we make a closure around the file contents. Then, the file privately creates a namespace and prevents name clashes between various libraries and modules in JavaScript.

Another benefit of this technique is enabling a simple alias creation for a global variable (which is easy to reference). We see this mainly with jQuery plugins because jQuery allows the disabling of reference $ to the namespace of jQuery, for example, jQuery.noConflict().

19. Can you list the benefits of 'use strict' at the start of a source file?

Example answer: First, the 'use strict' allows for strict error handling and parsing for the JavaScript code that always happens at runtime. The benefits of using it are:

• Prevention of accidental globals
• Removal of the 'this' coercion
• Easier debugging
• Strengthening the 'eval90' safety
• Preventing duplicate parameters (values)

20. What can you say about the types of JavaScript errors?

Example answer: There are three types of errors: Syntax, Runtime, and Logical.

Syntax errors (or parsing errors) happen during code interpretation, but that code is invalid regarding syntax. These common errors occur when we type a semicolon but want to type a double colon.

Runtime errors (exception errors) occur after compiling and interpreting and during runtime. They occur if we call a function that doesn't exist or isn't declared at that time. The syntax is error-free when this happens.

Logical errors occur when we face code issues, but the syntax is valid. We can run the program smoothly, but we'll notice something wrong at the end. This is a complex error type, hard to identify or resolve, and unrelated to the runtime. These errors occur when data flow is faulty, or the developer makes some script logic mistake.

Recognizing and selecting the best JavaScript Developer

Good and great developers are somewhat similar. However, a great JavaScript developer will have:

• More years of experience working with JavaScript and ES6+ versions

• Experienced in various JavaScript UI libraries and frameworks like React, Node, React Native, Angular, Vue, etc.

• More hands-on experience in game development, mobile app, and desktop app development

• Knowledge of the best IDE (integrated development environment)

• Better expertise with network services, backend web apps, and microservices

• A highly adaptable approach to their work

• Excellent results on their technical tests

Diamant here adds:

"Proficient JavaScript developers should also possess familiarity with advanced concepts, including but not limited to ES6+ features such as exponentiation and generators. In addition, a comprehensive evaluation of their problem-solving prowess within the JavaScript context is imperative, alongside an inquiry into their practical exposure to pertinent JavaScript frameworks and libraries, such as Angular, Vue, and React".

Also, a robust grasp of essential concepts and technologies, including the Document Object Model (DOM), Node.js, and package management tools like NPM or Yarn, is indispensable for a well-rounded expertise in JavaScript development.

Possible challenges during the hiring of a JavaScript developer

It is better to come prepared with alternatives and solutions for potential challenges. Here are some hiccups that might happen:

• No roadmap – Anything done without a plan or a systematic approach could fail later. Plan out every stage, anticipate every possible challenge, and store documents accordingly.

• Budget issues – Allocate enough for everyone involved in the hiring process for recruiters, hiring managers, and potential new team members. Set aside an extra budget for possible obstacles that could hinder the hiring.

• Candidate shortages – Remember that developer shortage is a common issue in the tech industry in recent years, further complicating how fast and efficiently you'll hire a great developer.

• Time to hire – Remember that the process might take longer than expected (if you skip the services that hire developers for you).

Industries where JavaScript is commonly used

JavaScript has versatile uses, but it is most widely used and famous for:

Finances

Many companies for payment processing and finances use JavaScript for their website's frontend. Payment apps made with JavaScript provide practical features for the financial sector of that business.

The apps are scalable, quick, and highly performative, crucial for payment processing businesses or anything financial-related.

Marketing and advertising

With JavaScript, it is easy to create visually appealing interactive effects that are the core of any good marketing relying on visuals. With the help of Google Analytics, JavaScript developers explore the advertising market and ensure a good user experience and successful ROI.

Healthcare

JavaScript developers efficiently work on the healthcare apps' data and its protection. They also work on the frontend of these apps to make them as simple as possible and maximally effective for all their users. One example is the healthcare billing apps, or apps for scheduling appointments.

eCommerce

In eCommerce, the user-friendly experience is more important than anything else. JavaScript developers efficiently work on simple app navigation so users can work through an app quickly (e.g., adding items to the shopping cart or arriving at checkout & payment sections).

Social media platforms

Social media platforms rely on JavaScript for both the frontend and backend. Also, developers know that if they disable JavaScript on a browser, the user won't be able to log into a particular social media account – all of this emphasizes how important JavaScript is for developers and users.

Business benefits of using JavaScript

This is why you need JavaScript for your business:

It's cost-efficient

Every business wants to save money in the long run. Developers that use JavaScript frameworks save time and effort on endless coding and tailor these frameworks to specific engagement needs. Also, many JavaScript frameworks are open-source, too.

It shows high-speed performance

On the client-side browser, JavaScript provides excellent performance and speed. We can quickly render an animation due to the server-side processing, ultimately enabling a seamless user experience.

It's fullstack-friendly

In JavaScript, developers can write both frontend and backend code. The MEAN stack of JavaScript (acronym – MongoDB, Express.js, Angular.js, Node.js) enables a seamless fullstack development.

It enables interoperability

Developers can use JavaScript to create various apps because this language pairs nicely with other programming languages.

It improves cybersecurity

Businesses need good cybersecurity, above all else, to protect their sensitive business data and user data. Developers can efficiently implement many helpful cybersecurity features that JavaScript frameworks offer.

It enables easy testing and debugging

It's easy for developers to recognize bugs early on because JavaScript is an interpreted language, and they can review the code by subsequent lines.

It's platform-independent

Almost every browser understands the JavaScript code quickly because this is an interpreted language and runs on all platforms or browsers.

It's excellent for creating well-designed interfaces

The JavaScript frameworks are the best choice if you want developers to create captivating interfaces, enabling a visually appealing and seamless user experience.

It has a broad developer support community

Like most popular programming languages, JavaScript has a broad community of excellent developers worldwide, always ready to share novelties, updates, or helpful development resources and tips.

Diamant sums up the beneficial aspects of JavaScript that every business owner needs to know:

1. Cross-platform compatibility – JavaScript can develop web, mobile, and desktop applications while reusing most codebases.

2. Interactive User Interfaces – JavaScript empowers businesses to create dynamic and interactive UI with real-time updates, animations, and transitions.

3. Rich web applications – We include frameworks of JavaScript, like React, Angular, and Vue, that allow businesses to build great-looking, feature-rich web and mobile applications.

4. Fast development – JavaScript's versatility, extensive libraries, and frameworks expedite development cycles, leading to a quicker time to develop features for your application.