JavaScript

Hire the Top 3% of Freelance JavaScript Developers

Toptal is a marketplace for top JavaScript developers and coders. CEOs, CTOs, and management at top companies and start-ups work with Toptal JavaScript freelancers to augment their development teams for JavaScript development, app development, web development, and other software development projects to achieve their business needs.

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Clients Rate Toptal JavaScript Developers4.3 / 5.0on average across 138 reviews as of Jun 13, 2023

Hire Freelance JavaScript Developers and Engineers

Jay Johnston

Freelance JavaScript Developer

United StatesToptal Member Since November 26, 2013

Coding HTML, CSS, and JavaScript since his armed forces days in 1997, Jay enjoys bringing value to clients via eCommerce solutions, legacy integrations, and optimized PHP and JavaScript-driven applications. His preferred DevOps environment is AWS, where he has strong skills in (and not limited to): Relational Database Services (RDS), Redshift, Dynamo DB, Data Migration Services (DMS), Lambda (serverless and microservices), Cloudwatch, Cloudtrail, and Event Bridge.

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Tyler Standley

Freelance JavaScript Developer

United StatesToptal Member Since August 3, 2018

Along with strong communication skills and an exemplary work ethic, Tyler brings his hands-on experience with a wide range of programming languages. Recently, though, his focus has been directed towards JavaScript libraries. Throughout his career, he’s worked on multiple agile teams as a core developer and is now interested in working on anything JavaScript-related.

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Justin Michela

Freelance JavaScript Developer

United StatesToptal Member Since June 26, 2018

Justin is a technical professional with a passion for learning and 18+ years of experience leading teams to build enterprise-grade distributed applications that solve real-world problems. He is a firm believer that collaboration across all facets of a business, from development to marketing to sales, is required to succeed in this endeavor.

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David Mihal

Freelance JavaScript Developer

United StatesToptal Member Since April 16, 2016

David has been developing websites and web applications for all of his adult life. As a software engineer, he's worked for many diverse software companies from early-stage startups to Google. David is experienced with many web frameworks and environments, but he particularly enjoys developing with Meteor.js. He appreciates the importance of quality code as well as the need to meet scheduling demands.

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James Koshigoe

Freelance JavaScript Developer

United StatesToptal Member Since April 2, 2014

James is a software engineer and consultant focused on web development. He has over a decade of experience in both startup and enterprise business environments building solutions where full-stack skills, creative thinking, and high attention to detail are key, and fast turnaround is paramount.

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Ahmad Soliman

Freelance JavaScript Developer

SpainToptal Member Since November 6, 2019

Starting as a Google intern, Ahmad has been leading the development of B2B services and admin web apps since 2015. On projects, he typically makes the architectural decisions about state management, framework selection, testing strategies, folder structure, team load and task allocation, and mentoring junior developers. Ahmad also has built shared UI components libraries, reusable CSS code, higher-order components, and best practices for scalable and maintainable codebases.

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Ricardo Basto

Freelance JavaScript Developer

GermanyToptal Member Since May 7, 2019

Ricardo has been coding for over 20 years, having worked on projects in more than ten programming languages. He has co-founded companies, worked in a few successful startups as CTO, and managed distributed teams of developers and product designers. His recent work has ranged from data science and machine learning to high-performing web and mobile applications, including Web3 and crypto.

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Stepan Anokhin

Freelance JavaScript Developer

RussiaToptal Member Since March 5, 2019

With a solid mathematical knowledge base and a professional software developer background, Stepan has the experience and skills to fulfill most software engineering role. During his professional career, he's worked on various projects including large enterprise systems, web development, and cloud computing. Stepan is always eager to explore new areas in computer science and apply bleeding-edge technologies.

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Anton Razmakhnin

Freelance JavaScript Developer

RussiaToptal Member Since December 19, 2019

Anton is a senior C# developer with over ten years of experience developing both native (WinForms, WPF) and web (ASP.NET) applications for .NET and .NET Core platforms. He has expertise in leading teams, mentoring developers, automating processes, and developing web applications' front-end. He writes exceptionally clean code and is a stickler for testing, ensuring accuracy and stability.

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Davor Badrov

Freelance JavaScript Developer

CroatiaToptal Member Since December 12, 2019

Davor is a senior full-stack developer with 9+ years of experience, skilled in crafting scalable and efficient solutions. Proficient in both monolithic and microservice architectures, Davor is a versatile asset to any team and project with a deep understanding of front-end and back-end technologies. With a passion for problem-solving and constant learning, he is the perfect candidate to drive your company's growth.

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Abdelhamid Attaby

Freelance JavaScript Developer

EgyptToptal Member Since December 12, 2019

Abdelhamid is a former GitHub professional software engineer with 13+ years of experience and a master's degree and PhD in computer science and engineering. He also worked in executive and leadership positions for different small and medium startups. Abdelhamid's specialties include JavaScript, TypeScript, Node.js, Python, REST API, GraphQL, Redis, NoSQL, SQL, React, Next.js, microservices, CI/CD, and cloud services.

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A Hiring Guide

Guide to Hiring a Great JavaScript Developer

As with any technology, there’s knowing JavaScript and then there’s really knowing JavaScript. Here are proven, effective techniques and questions for finding true masters of the language.

Read Hiring Guide

JavaScript Hiring Resources

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Brantley Pace, CEO & Co-Founder

Tripcents

I am more than pleased with our experience with Toptal. The professional I got to work with was on the phone with me within a couple of hours. I knew after discussing my project with him that he was the candidate I wanted. I hired him immediately and he wasted no time in getting to my project, even going the extra mile by adding some great design elements that enhanced our overall look.

Paul Fenley, Director

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The developers I was paired with were incredible -- smart, driven, and responsive. It used to be hard to find quality engineers and consultants. Now it isn't.

Ryan Rockefeller, CEO

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Toptal understood our project needs immediately. We were matched with an exceptional freelancer from Argentina who, from Day 1, immersed himself in our industry, blended seamlessly with our team, understood our vision, and produced top-notch results. Toptal makes connecting with superior developers and programmers very easy.

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As a small company with limited resources we can't afford to make expensive mistakes. Toptal provided us with an experienced programmer who was able to hit the ground running and begin contributing immediately. It has been a great experience and one we'd repeat again in a heartbeat.

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We used Toptal to hire a developer with extensive Amazon Web Services experience. We interviewed four candidates, one of which turned out to be a great fit for our requirements. The process was quick and effective.

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Photo Kharma

Sergio was an awesome developer to work with. Top notch, responsive, and got the work done efficiently.

Dennis Baldwin, Chief Technologist and Co-Founder

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Working with Marcin is a joy. He is competent, professional, flexible, and extremely quick to understand what is required and how to implement it.

André Fischer, CTO

POSTIFY

We needed a expert engineer who could start on our project immediately. Simanas exceeded our expectations with his work. Not having to interview and chase down an expert developer was an excellent time-saver and made everyone feel more comfortable with our choice to switch platforms to utilize a more robust language. Toptal made the process easy and convenient. Toptal is now the first place we look for expert-level help.

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Networld Media Group

Toptal's developers and architects have been both very professional and easy to work with. The solution they produced was fairly priced and top quality, reducing our time to launch. Thanks again, Toptal.

Jeremy Wessels, CEO

Kognosi

We had a great experience with Toptal. They paired us with the perfect developer for our application and made the process very easy. It was also easy to extend beyond the initial time frame, and we were able to keep the same contractor throughout our project. We definitely recommend Toptal for finding high quality talent quickly and seamlessly.

Ryan Morrissey, CTO

Applied Business Technologies, LLC

I'm incredibly impressed with Toptal. Our developer communicates with me every day, and is a very powerful coder. He's a true professional and his work is just excellent. 5 stars for Toptal.

Pietro Casoar, CEO

Ronin Play Pty Ltd

Working with Toptal has been a great experience. Prior to using them, I had spent quite some time interviewing other freelancers and wasn't finding what I needed. After engaging with Toptal, they matched me up with the perfect developer in a matter of days. The developer I'm working with not only delivers quality code, but he also makes suggestions on things that I hadn't thought of. It's clear to me that Amaury knows what he is doing. Highly recommended!

George Cheng, CEO

Bulavard, Inc.

As a Toptal qualified front-end developer, I also run my own consulting practice. When clients come to me for help filling key roles on their team, Toptal is the only place I feel comfortable recommending. Toptal's entire candidate pool is the best of the best. Toptal is the best value for money I've found in nearly half a decade of professional online work.

Ethan Brooks, CTO

Langlotz Patent & Trademark Works, Inc.

In Higgle's early days, we needed the best-in-class developers, at affordable rates, in a timely fashion. Toptal delivered!

Lara Aldag, CEO

Higgle

Toptal makes finding a candidate extremely easy and gives you peace-of-mind that they have the skills to deliver. I would definitely recommend their services to anyone looking for highly-skilled developers.

Michael Gluckman, Data Manager

Mxit

Toptal’s ability to rapidly match our project with the best developers was just superb. The developers have become part of our team, and I’m amazed at the level of professional commitment each of them has demonstrated. For those looking to work remotely with the best engineers, look no further than Toptal.

Laurent Alis, Founder

Livepress

Toptal makes finding qualified engineers a breeze. We needed an experienced ASP.NET MVC architect to guide the development of our start-up app, and Toptal had three great candidates for us in less than a week. After making our selection, the engineer was online immediately and hit the ground running. It was so much faster and easier than having to discover and vet candidates ourselves.

Jeff Kelly, Co-Founder

Concerted Solutions

We needed some short-term work in Scala, and Toptal found us a great developer within 24 hours. This simply would not have been possible via any other platform.

Franco Arda, Co-Founder

WhatAdsWork.com

Toptal offers a no-compromise solution to businesses undergoing rapid development and scale. Every engineer we've contracted through Toptal has quickly integrated into our team and held their work to the highest standard of quality while maintaining blazing development speed.

Greg Kimball, Co-Founder

nifti.com

How to Hire JavaScript Developers through Toptal

1

Talk to One of Our Industry Experts

A Toptal director of engineering will work with you to understand your goals, technical needs, and team dynamics.
2

Work With Hand-Selected Talent

Within days, we'll introduce you to the right JavaScript developer for your project. Average time to match is under 24 hours.
3

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Work with your new JavaScript developer for a trial period (pay only if satisfied), ensuring they're the right fit before starting the engagement.

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FAQs

  • How are Toptal JavaScript developers different?

    At Toptal, we thoroughly screen our JavaScript developers to ensure we only match you with talent of the highest caliber. Of the more than 100,000 people who apply to join the Toptal network each year, fewer than 3% make the cut. You'll work with engineering experts (never generalized recruiters or HR reps) to understand your goals, technical needs, and team dynamics. The end result: expert vetted talent from our network, custom matched to fit your business needs. Start now.

  • Can I hire JavaScript developers in less than 48 hours through Toptal?

    Depending on availability and how fast you can progress, you could start working with a JavaScript developer within 48 hours of signing up. Start now.

  • What is the no-risk trial period for Toptal JavaScript developers?

    We make sure that each engagement between you and your JavaScript developer begins with a trial period of up to two weeks. This means that you have time to confirm the engagement will be successful. If you're completely satisfied with the results, we'll bill you for the time and continue the engagement for as long as you'd like. If you're not completely satisfied, you won't be billed. From there, we can either part ways, or we can provide you with another expert who may be a better fit and with whom we will begin a second, no-risk trial. Start now.

  • What type of talent does Toptal have?

    Our platform hosts a very diverse range of skill sets, experiences, and backgrounds. Our freelancers range from software engineers, user experience designers, project management experts, and product managers to finance experts who have worked at leading companies such as Google, Microsoft, Amazon, and many more.

  • What other services does Toptal provide?

    Besides our talent matching services, we also provide web and application development services like a development company. Through our Toptal Projects team, we assemble cross-functional teams of senior project managers, web developers, app developers, user interface designers, and other technical skills. Our team members follow a well-defined development process to build a fully functional solution.

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JavaScript

How to Hire a Great JavaScript Developer

The Challenge

In today’s technology landscape, JavaScript has essentially become synonymous with client-side web development and now, with the advent of technologies and JavaScript frameworks like Node.js, Vue.js, and React.js, JavaScript is becoming a dominant server side technology as well.

Accordingly, full-stack developer resumes that reference at least some degree of JavaScript experience have essentially become universal in the software development community. This makes locating JavaScript web developers fairly easy, but makes sifting through them to find “the elite few” that much more of a challenge. Finding them requires a highly-effective recruiting process, as described in our post In Search of the Elite Few – Finding and Hiring the Best Developers in the Industry. Such a process can then be augmented with questions – such as those presented herein – to identify those sparsely distributed candidates across the globe who are true JavaScript experts.

Yeah, I know JavaScript…

As with any technology, there’s knowing JavaScript development and then there’s really knowing JavaScript. In our search for true masters of the language, we require an interview process that can accurately quantify a candidate’s position along the continuum of JavaScript expertise levels.

Toward that goal, this post offers a sampling of questions that are key to evaluating the breadth and depth of a candidate’s mastery of JavaScript. It is important to bear in mind, though, that these sample questions are intended merely as a guide. Not every “A” candidate worth hiring will be able to properly answer them all, nor does answering them all guarantee an “A” candidate. At the end of the day, hiring remains as much of an art as it does a science.

Assessing the Foundation

It's far too common to encounter 'experienced' JavaScript programmers whose grasp of the fundamentals of the language is either weak or confused.

JavaScript is a prototype-based scripting language with dynamic typing. JavaScript can, at first, be a bit confusing for developers experienced in class-based languages (such as Java or C++), as it is dynamic and does not provide a traditional class implementation. It’s therefore far too common to encounter ‘experienced’ JS developers whose grasp of the fundamentals of the language is either weak or confused.

Questions that can help assess a developer’s grasp of JavaScript fundamentals, including some of its more subtle nuances, are therefore an important component of the interview process. Here are some examples…

Q: Describe inheritance and the prototype chain in JavaScript. Give an example.

Although JavaScript is an object-oriented language, it is prototype-based and does not implement a traditional class-based inheritance system.

In JavaScript, each object internally references another object, called its prototype. That prototype object, in turn, has a reference to its prototype object, and so on. At the end of this prototype chain is an object with null as its prototype. The prototype chain is the mechanism by which inheritance – prototypal inheritance to be precise – is achieved in JavaScript. In particular, when a reference is made to a property that an object does not itself contain, the prototype chain is traversed until the referenced property is found (or until the end of the chain is reached, in which case the property is undefined).

Here’s a simple example:

function Animal() { this.eatsVeggies = true; this.eatsMeat = false; }

function Herbivore() {}
Herbivore.prototype = new Animal();

function Carnivore() { this.eatsMeat = true; }
Carnivore.prototype = new Animal();

var rabbit = new Herbivore();
var bear = new Carnivore();

console.log(rabbit.eatsMeat);   // logs "false"
console.log(bear.eatsMeat);     // logs "true"

Q: Compare and contrast objects and hashtables in JavaScript.

This is somewhat of a trick question since, in JavaScript, objects essentially are hashtables; i.e., collections of name-value pairs. In these name-value pairs, a crucial point to be aware of is that the names (a.k.a., keys) are always strings. And that actually leads us to our next question…

Q: Consider the code snippet below (source). What will the alert display? Explain your answer.

var foo = new Object();
var bar = new Object();
var map = new Object();

map[foo] = "foo";
map[bar] = "bar";

alert(map[foo]);  // what will this display??

It is the rare candidate who will correctly answer that this alerts the string “bar”. Most will mistakenly answer that it alerts the string “foo”. So let’s understand why “bar” is indeed the correct, albeit surprising, answer…

As mentioned in the answer to the prior question, a JavaScript object is essentially a hashtable of name-value pairs where the names (i.e., keys) are strings. And they are always strings. In fact, when an object other than a string is used as a key in JavaScript, no error occurs; rather, JavaScript silently converts it to a string and uses that value as the key instead. This can have surprising results, as the above code demonstrates.

To understand the above code snippet, one must first recognize that the map object shown does not map the object foo to the string “foo”, nor does it map the object bar to the string “bar”. Since the objects foo and bar are not strings, when they are used as keys for map, JavaScript automatically converts the key values to strings using each object’s toString() method. And since neither foo nor bar defines its own custom toString() method, they both use the same default implementation. That implementation simply generates the literal string “[object Object]” when it is invoked. With this explanation in mind, let’s re-examine the code snippet above, but this time with explanatory comments along the way:

var foo = new Object();
var bar = new Object();
var map = new Object();

map[foo] = "foo";    // --> map["[object Object]"] = "foo";
map[bar] = "bar";    // --> map["[object Object]"] = "bar";
                     // NOTE: second mapping REPLACES first mapping!

alert(map[foo]);     // --> alert(map["[object Object]"]);
                     // and since map["[object Object]"] = "bar",
                     // this will alert "bar", not "foo"!!
                     //    SURPRISE! ;-)

Q: Explain closures in JavaScript. What are they? What are some of their unique features? How and why might you want to use them? Provide an example.

A closure is a function, along with all variables or functions that were in-scope at the time that the closure was created. In JavaScript, a closure is implemented as an “inner function”; i.e., a function defined within the body of another function. Here is a simplistic example:

(function outerFunc(outerArg) {
  var outerVar = 3;

  (function middleFunc(middleArg) {
    var middleVar = 4;

    (function innerFunc(innerArg) {
      var innerVar = 5;
      // EXAMPLE OF SCOPE IN CLOSURE:
      // Variables from innerFunc, middleFunc, and outerFunc,
      // as well as the global namespace, are ALL in scope here.
      console.log("outerArg="+outerArg+
                  " middleArg="+middleArg+
                  " innerArg="+innerArg+"\n"+
                  " outerVar="+outerVar+
                  " middleVar="+middleVar+
                  " innerVar="+innerVar);
      // --------------- THIS WILL LOG: ---------------
      //    outerArg=123 middleArg=456 innerArg=789
      //    outerVar=3 middleVar=4 innerVar=5
    })(789);
  })(456);
})(123);

An important feature of closures is that an inner function still has access to the outer function’s variables even after the outer function has returned. This is because, when functions in JavaScript execute, they use the scope that was in effect when they were created.

A common point of confusion that this leads to, though, is based on the fact that the inner function accesses the values of the outer function’s variables at the time it is invoked (rather than at the time that it was created). To test the candidate’s understanding of this nuance, present the following code snippet that dynamically creates five buttons and ask what will be displayed when the user clicks on the third button:

function addButtons(numButtons) {
  for (var i = 0; i < numButtons; i++) {
    var button = document.createElement('input');
    button.type = 'button';
    button.value = 'Button ' + (i + 1);
    button.onclick = function() {
      alert('Button ' + (i + 1) + ' clicked');
    };
    document.body.appendChild(button);
    document.body.appendChild(document.createElement('br'));
  }
}

window.onload = function() { addButtons(5); };

Many will mistakenly answer that “Button 3 clicked” will be displayed when the user clicks on the third button. In fact, the above code contains a bug (based on a misunderstanding of the way closures work) and “Button 6 clicked” will be displayed when the user clicks on any of the five buttons. This is because, at the point that the onclick method is invoked (for any of the buttons), the for loop has already completed and the variable i already has a value of 5.

An important follow-up question is to ask the candidate how to fix the bug in the above code, so as to produce the expected behavior (i.e., so that clicking on button n will display “Button n clicked”). The correct answer, which demonstrates proper use of closures, is as follows:

function addButtons(numButtons) {
  for (var i = 0; i < numButtons; i++) {
    var button = document.createElement('input');
    button.type = 'button';
    button.value = 'Button ' + (i + 1);
    // HERE'S THE FIX:
    // Employ the Immediately-Invoked Function Expression (IIFE)
    // pattern to achieve the desired behavior:
    button.onclick = function(buttonIndex) {
      return function() {
        alert('Button ' + (buttonIndex + 1) + ' clicked');
      };
    }(i);
    document.body.appendChild(button);
    document.body.appendChild(document.createElement('br'));
  }
}

window.onload = function() { addButtons(5); };

Although by no means exclusive to JavaScript, closures are a particularly useful construct for many modern day JavaScript programming paradigms. They are used extensively by some of the most popular JavaScript libraries, such as jQuery and Node.js.

Embracing Diversity

JavaScript accommodates an unusually wide array of programming techniques and design patterns. A JavaScript master will be well aware of the significance and ramifications of choosing one approach vs. another.

A multi-paradigm language, JavaScript supports object-oriented, imperative, and functional programming styles. As such, JavaScript accommodates an unusually wide array of programming techniques and design patterns. A JavaScript master will be well aware of the existence of these alternatives and, more importantly, the significance and ramifications of choosing one approach over another. Here are a couple of sample questions that can help gauge this dimension of a candidate’s expertise:

Q: Describe the different ways of creating objects and the ramifications of each. Provide examples.

The graphic below contrasts various ways in JavaScript to create objects and the differences in the prototype chains that result from each.

Q: Is there ever any practical difference between defining a function as a function expression (e.g., var foo = function(){}) or as a function statement (e.g., function foo(){})? Explain your answer.

Yes, there is a difference, based on how and when the value of the function is assigned.

When a function statement (e.g., function foo(){}) is used, the function foo may be referenced before it has been defined, through a technique known as “hoisting”. A ramification of hoisting is that the last definition of the function is the one that will be employed, regardless of when it is referenced (if that’s not clear, the example code below should help clarify things).

In contrast, when a function expression (e.g., var foo = function(){}) is used, the function foo may not be referenced before it is defined, just like any other assignment statement. Because of this, the most recent definition of the function is the one that will be employed (and accordingly, the definition must precede the reference, or the function will be undefined).

Here’s a simple example that demonstrates the practical difference between the two. Consider the following code snippet:

function foo() { return 1; }

alert(foo());   // what will this alert?

function foo() { return 2; }

Many JavaScript developers will mistakenly answer that the above alert will display “1” and will be surprised to learn that it will in fact display “2”. As described above, this is due to hoisting. Since a function statement was used to define the function, the last definition of the function is the one that is hoisted at the time it is invoked (even though it is subsequent to its invocation in the code!).

Now consider the following code snippet:

var foo = function() { return 1; }

alert(foo());   // what will this alert?

foo = function() { return 2; }

In this case, the answer is more intuitive and the alert will display “1” as expected. Since a function expression was employed to define the function, the most recent definition of the function is the one that is employed at the time it is invoked.

The Devil’s in the Details

In addition to the advanced JavaScript concepts discussed thus far, there are a number of lower-level syntactical details of the language that a true JavaScript guru will be intimately familiar with. Here are a few examples…

Q: What is the significance of, and reason for, wrapping the entire content of a JavaScript source file in a function block?

This is an increasingly common practice, employed by many popular JavaScript libraries (jQuery, Node.js, etc.). This technique creates a closure around the entire contents of the file which, perhaps most importantly, creates a private namespace and thereby helps avoid potential name clashes between different JavaScript modules and libraries.

Another feature of this technique is to allow for an easily referenceable (presumably shorter) alias for a global variable. This is often used, for example, in jQuery plugins. jQuery allows you to disable the $ reference to the jQuery namespace, using jQuery.noConflict(). If this has been done, your code can still use $ employing this closure technique, as follows:

(function($) { /* jQuery plugin code referencing $ */ } )(jQuery);

Q: What is the difference between == and ===? Between != and !==? Give an example.

The difference between “triple” comparison operators (===, !==) and double comparison operators (==, !=) in JavaScript is that double comparison operators perform implicit type conversion on the operands before comparing them whereas, with the triple comparison operators, no type conversion is performed (i.e., the values must be equal and the types must be the same for the operands to be considered equal).

As a simple example, the expression 123 == '123' will evaluate to true, whereas 123 === '123' will evaluate to false.

Q: What is the significance of including 'use strict' at the beginning of a JavaScript source file?

Though there is much more to be said on the topic, the short and most important answer here is that use strict is a way to voluntarily enforce stricter parsing and error handling on your JavaScript code at runtime. Code errors that would otherwise have been ignored or would have failed silently will now generate errors or throw exceptions. In general, it is a good practice.

Wrap Up

JavaScript is perhaps one of the most misunderstood and underestimated programming languages in existence today. The more one peels the JavaScript onion, the more one realizes what is possible. JavaScript is versatile enough to be used by front-end and back-end developers. Accordingly, finding true masters of the language for full-time or part-time roles in the United States or abroad is a challenge. We hope you find the questions presented in this post to be a useful foundation for “separating the wheat from the chaff” in your quest for the “elite few” among the best JavaScript developers to add to your development team.

Top JavaScript Developers are in High Demand.

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