Trusted by

Hire JavaScript developers and engineers

Harold Frazier, Jr., United States

Member since September 5, 2012
Computers have been Harold's passion since he compiled his first program in elementary school. He will always appreciate how the software industry continues to change and grow through technology innovations that make our lives more enjoyable and efficient. Click to continue

Ryan J. Peterson, United States

Member since June 18, 2013
Ryan is a top architect, entrepreneur, and developer. He boasts a proven competency in building cloud-scalable, extensible software and systems. He writes code that can be maintained and expanded over time as business systems and requirements adapt to market demands or pivots in core business direction. Click to continue

Rafael Chiti, United Kingdom

Member since May 8, 2014
Rafael is passionate about change and trying new things, both professionally and in general with his life. He is a skilled web developer with over 8 years of experience. He loves startups and is extremely proactive. Click to continue

Igor Oleinikov, Canada

Member since August 7, 2013
Igor is an architect and lead developer with extensive development experience in the .NET technology stack (including C# and MVC), as well as JavaScript/TypeScript. With a passion for programming, he spends his free time exploring the latest technologies. Click to continue

Jasmin Ibrisimbegovic, Bosnia and Herzegovina

Member since April 2, 2014
As a certified Microsoft Developer, Jasmin has been coding since the 1990s. His areas of expertise are desktop and web applications that are built on the .NET platform. In the last 2 years, he has devoted special attention to the development of mobile applications for Android using Java. Click to continue

Richard Smuts, South Africa

Member since July 30, 2014
Richard is a friendly, well-spoken, outgoing, intelligent individual who enjoys problem-solving. He carefully assesses the requirements of a task, taking the opportunity to think it through and working efficiently to produce easily maintainable and complete products. Click to continue

Raoni Boaventura, Brazil

Member since March 9, 2012
Raoni is an experienced software developer and who has contributed to a wealth of projects using Ruby on Rails, JavaScript, and PHP on top of many other programming languages and frameworks. He is an excellent problem solver, and a great communicator as both a team member and a team lead. Click to continue

Rahul Devaskar, Australia

Member since July 30, 2014
Rahul is a professional software engineer with leadership experience and expertise in building full-stack Node.js applications and streaming data analytics solutions. He has designed and developed an innovative context-aware advertising platform using Node.js and machine learning techniques. This platform was acquired by a Silicon Valley-based data analytics company. Click to continue

Rafal Gwizdala, Poland

Member since July 21, 2014
Rafal is a skilled software engineer with strong architecture and coding skills, broad technology knowledge, and many years of experience delivering software. He is a project leader, mentor, coder, and consultant. He specializes in business software, process automation, and transactional systems. Click to continue

Anna Chiara Bellini, Italy

Member since August 5, 2013
When Anna was a kid, her brother got a Commodore 64 for Christmas. He played video games, and she started coding. Since then, her career has spanned many different projects and programming technologies. But regardless of the task at hand, she always brings the same enthusiasm and passion. Click to continue
JavaScript Resources
Trustpilot
Toptal on TV
"Toptal is killing it, it kind of owns this market."
Andrew Ross Sorkin Reviews Toptal
Cnbc 02e66b
"Tech companies simply cannot find the quality employees they want to hire. The solution: Toptal."
Liz Claman´s Review of Toptal
Fox 7ef901
Toptal in the press
"Passing Toptal's screening process gives you unparalleled access to meaningful projects with great clients."
Anna Johansson
"Toptal's approach makes it a definite outlier compared to conventional platforms."
Drew Hendricks
A hiring guide
The Vital Guide to JavaScript Interviewing

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.

Testimonials
“I've gotten 1 developer from Toptal so far. He's a really good part of our team. I'm planning on adding another from Toptal in the near future. Toptal is a big help these days when recruiting is a big part of my job.”
Aaron Rubin @ ShipHero
“Toptal was the best thing to happen to my web app. Initially, I hired a team of freelancers from India through another freelancing website—which was a nightmare. In fact, it was so bad that I had to start again from scratch, which is when I found Toptal. The experiences were like night and day. It was so refreshing to get partnered up with a quality developer that I could trust due to Toptal's extensive screening process. I will only use Toptal from now on and highly recommend you do the same.”
Chris Holtzhauer
CEO @ HootRecruit
“Prior to working with Toptal, we had a very difficult time finding qualified developers. The Toptal team worked with us to find a developer that was a great fit in terms of technical skills, culture, and finances. Our Toptal developer is four months into this project and we are still impressed with the attention to detail and technical prowess that he brings to our team.”
Justin Fister
Chief Scientist @ PaperRater
“Chris Wood is an absolutely exceptional Python developer, and the single most efficient programmer I've ever worked with. From the beginning of the project, Chris was instantly a vital member of the team. He's proactive, self-managed, knowledgeable, and efficient. I point him in a direction, and he delivers. Chris will be a part of the Crisis Cleanup team as long as I have anything to say about it.”
Aaron Titus
Project Manager @ Crisis Cleanup
“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
“Back in July '12, FundedByMe needed to quickly scale our development team to create the equity crowdfunding leg of our operation. Working with a small budget, we couldn't spend time on vetting candidates, so we turned to Toptal. They identified a stellar developer that truly set the bar when it came to delivering product.”
Arno Smit
CTO @ FundedByMe.com
“After some mixed experiences with other freelancing sites, I decided to give Toptal a try. I'm three weeks in, and so far my experience has been top-notch. The trial period was a great way to get familiar with my developer and grow confident in his abilities. Since then, Robert has continued to meet and exceed my expectations with quality work, strong communication, and a great attitude.”
CEO @ uTru.st
“The task of finding and hiring the right developers and programmers can be daunting, especially for startups. After sifting through countless unfit freelancers, we came across Toptal. They were able to fill our open position in no time, and I'd highly recommend the service!”
Josef Holm
CEO @ Tubestart
“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
“We used Toptal to hire a developer with extensive Amazon Web Services experience. The process was quick and effective. We interviewed four candidates one of which turned out to be a great fit for our requirements. We plan to use Toptal again in the future and would recommend their services.”
Abner Guzmán Rivera
CTO and Chief Scientist @ PhotoKarma, Inc.
“Dario was recently assigned to our company in order to help with PHP and JW Video player refinements. He listens extremely well and offers common sense suggestions that save both time and money. He speeds up the process by asking great questions, and he just delivered our first project on time. His redesigned player offers a very pleasing appearance and delivers functions that are both elegant and intuitive.”
Dennis B. Jacobs
“Toptal is amazing! Sourcing and interviewing candidates has always been incredibly cumbersome and difficult - and usually takes weeks or months to find the right people. With Toptal, we had 5 candidates in 2 days that were all perfect for the job. They made the scheduling of interviews easy and straightforward and we were working with a top-level bad-ass developer within 2 weeks. I love you, Toptal.”
Ian Fosbery
“We had a wonderful experience with our Toptal consultant. He was very reliable and punctual, delivering excellent work on a budget—we will certainly be using him again!”
Barbara Karpf
President @ DecoratorsBest
“Dario was recently assigned to our company in order to help with PHP and JW Video player refinements. He listens well and offers common sense suggestions that save both time and money. Dario speeds up the process by asking questions and has delivered our first project on time. His redesigned player offers a very pleasing appearance and delivers functions that are both ergonomic and intuitive.”
Dennis B. Jacobs
President @ College TV Ticket
“Ignacio is one of the most diligent software developers that we have ever worked with—we feel like he's part of the family. He has always been flexible enough to work on our team's schedule and never misses deadlines. Toptal gets you the talent you need, on your timeline, keeping the process very low friction.”
Austin Evarts
CEO @ GoChime
“Finding a good developer who specialised in the technologies we use seemed like an impossible task... until we used Toptal. We had several trial periods and have just accepted our first developer to join the team! The whole process went seamlessly and without any surprises or hidden costs. We are very happy and will continue to work together!”
Artem Tolmachev
CEO @ eKids.nl
“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 devoted to the project. We definitely recommend Toptal for finding high quality talent quickly and seamlessly.”
Ryan Morrissey
CTO @ Applied Business Technologies, LLC
“After my hard drive crashed, I needed a quick script to recover my data, which was crucial to my research. After almost three weeks struggling with freelancers, I was ready to try Toptal. It turned out to be the right move: even if a little more expensive, my developer, Chatri, was highly punctual and got the job done in a quick, painless, and focused manner. Thanks, Chatri!”
Rob Ellis
“Our Toptal contractor quickly came up to speed on our process and became an integrated part of our team. We look forward to growing together!”
Vitaly M. Golomb
CEO @ Keen Systems
Hire a top JavaScript developer now.
Toptal is a marketplace for top JavaScript developers, engineers, programmers, coders, architects, and consultants. Top companies and start-ups choose Toptal freelancers for their mission critical software projects.
Full
profile
Harold Frazier, Jr.United States
Computers have been Harold's passion since he compiled his first program in elementary school. He will always appreciate how the software industry continues to change and grow through technology innovations that make our lives more enjoyable and efficient.
[click to continue…]
JavaScriptSQLC#C++HTML5JavaAndroid SDKAndroid StudioWindows MobileAndroid
Hire
Full
profile
Ryan J. PetersonUnited States
Ryan is a top architect, entrepreneur, and developer. He boasts a proven competency in building cloud-scalable, extensible software and systems. He writes code that can be maintained and expanded over time as business systems and requirements adapt to market demands or pivots in core business direction.
[click to continue…]
JavaScriptHTML5PHPCakePHPAngularJSKnockout.jsAngularUINode.jsjQuery UIjQueryAgile Software DevelopmentMac OS XMySQL
Hire
Full
profile
Rafael ChitiUnited Kingdom
Rafael is passionate about change and trying new things, both professionally and in general with his life. He is a skilled web developer with over 8 years of experience. He loves startups and is extremely proactive.
[click to continue…]
JavaScriptCSSjQueryReact.jsAgile Software DevelopmentMac OS
Hire
Full
profile
Igor OleinikovCanada
Igor is an architect and lead developer with extensive development experience in the .NET technology stack (including C# and MVC), as well as JavaScript/TypeScript. With a passion for programming, he spends his free time exploring the latest technologies.
[click to continue…]
JavaScriptC#C++/CLIC/C++SQLHTML5ASP.NET MVCKnockout.js.NETAngularJSjQuery UIReact.jsjQuery
Hire
Full
profile
Jasmin IbrisimbegovicBosnia and Herzegovina
As a certified Microsoft Developer, Jasmin has been coding since the 1990s. His areas of expertise are desktop and web applications that are built on the .NET platform. In the last 2 years, he has devoted special attention to the development of mobile applications for Android using Java.
[click to continue…]
JavaScriptSQLVB.NETC#.NET.NETVisual StudioAndroid StudioAndroidMySQL
Hire
Full
profile
Richard SmutsSouth Africa
Richard is a friendly, well-spoken, outgoing, intelligent individual who enjoys problem-solving. He carefully assesses the requirements of a task, taking the opportunity to think it through and working efficiently to produce easily maintainable and complete products.
[click to continue…]
JavaScriptHTML5C#CSSASP.NET Web API 2.NETAngularJSASP.NET MVCASP.NET Web APIjQuery.NET BCLVisual StudioWeb App Development
Hire
Full
profile
Raoni BoaventuraBrazil
Raoni is an experienced software developer and who has contributed to a wealth of projects using Ruby on Rails, JavaScript, and PHP on top of many other programming languages and frameworks. He is an excellent problem solver, and a great communicator as both a team member and a team lead.
[click to continue…]
JavaScriptC++RubyCoffeeScriptPHPCSS3HTML5Twitter BootstrapAngularJSRuby on RailsjQueryFacebook APIjQuery UI
Hire
Full
profile
Rahul DevaskarAustralia
Rahul is a professional software engineer with leadership experience and expertise in building full-stack Node.js applications and streaming data analytics solutions. He has designed and developed an innovative context-aware advertising platform using Node.js and machine learning techniques. This platform was acquired by a Silicon Valley-based data analytics company.
[click to continue…]
JavaScriptCoffeeScriptAngularJSNode.jsMac OS X
Hire
Full
profile
Rafal GwizdalaPoland
Rafal is a skilled software engineer with strong architecture and coding skills, broad technology knowledge, and many years of experience delivering software. He is a project leader, mentor, coder, and consultant. He specializes in business software, process automation, and transactional systems.
[click to continue…]
JavaScriptC#ASP.NET MVCASP.NETVisual StudioWindowsSQL Server
Hire
Full
profile
Anna Chiara BelliniItaly
When Anna was a kid, her brother got a Commodore 64 for Christmas. He played video games, and she started coding. Since then, her career has spanned many different projects and programming technologies. But regardless of the task at hand, she always brings the same enthusiasm and passion.
[click to continue…]
JavaScriptSQLJavaStrutsSpringSpring MVCJava ServletsMicrosoft ExcelJava SEJava EE
Hire

The Vital Guide to JavaScript Interviewing

The Challenge

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

Accordingly, resumes that reference at least some degree of JavaScript experience have essentially become universal in the software development community. This makes locating JavaScript 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 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 developers 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’ JavaScript 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. Accordingly, finding true masters of the language 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 JavaScript developers.

Hire JavaScript developers now
Alvaro 1506e7

My team is going to personally help you find the best candidate to join your team.

Alvaro Oliveira
VP of Talent Operations