Webassembly vs. JavaScript: How Do They Compare


JavaScript is huge!

It's everywhere, powering web browsers and running on phones, tablets, desktops, servers – the list goes on, but you get the point.

Released in 1995, JavaScript (abbreviated as JS) is an object-oriented, single-threaded scripting language that runs natively in the browser. It is the most popular programming language on the web, used by over 60% of developers, according to Statista.

JS’ dynamic nature is its most significant selling point, but it has been a double-edged sword, making it clunky to run complex projects at a high-performance level.

In recent years, a new natively supported programming language has seen the days; WebAssembly (abbreviated as WASM). But how do WebAssembly vs. JavaScript compare?

Can WASM become the next dominant language in web development and dethrone JavaScript as the supreme web language?

Not necessarily, but that doesn’t mean that WebAssembly isn’t worth a look –and probably even more than that.

In this article, we take a long hard look at WebAssembly, how it works, what makes it different from JavaScript, and the last burning question: is it better than JavaScript, or should you simply learn both?

A Quick Intro To JavaScript

JavaScript unofficial logo

Back in 1995, Brendan Eich, the creator of JavaScript, was working for Netscape, the makers of the arguably best browser at the time –I remember using Netscape in 1997 when the internet reached my neighborhood in Venezuela. My six-year-old self liked it, but don’t take his word for granted.

Eich’s aimed at developing a scripting language that would make it simple to construct components and automate interactions. This would turn the browser into a full-fledged application platform. This quest for simplicity drives Javascript's simple syntax and structure, making it one of the easiest languages to learn.

JS is dynamic by nature. Although it’s mainly used for building web pages, –97.6% of websites use JavaScript as a client-side programming language– developers can also use it for non-browser environments like embedded systems and databases. Interestingly, most developers discover JavaScript via frameworks and libraries like React, VueJS, or Angular, making it easy to build interactive web pages. In JavaScript, a browser executes code using the JavaScript engine, which comprises the memory stack that allocates memory and the call stack that keeps track of the program. This engine is a popular type of Google’s v8 engine used by Chrome and Node.js’ server-side framework.

Aside from the JS engine, additional browser capabilities such as Web APIs and the event loop are available. Developers can interact with these capabilities at runtime using JS features governed by the ECMAScript Standard.

JavaScript Concepts

  • Variables: Allow you to assign and store values. There are currently three ways of declaring a variable: Var, Let, and Const. ES6 introduced the last two.

var x = 10;
let country = ‘Argentina;
const pi = 3.14;
  • Objects: Store properties and values.

let orange = {
  type: “fruit”;
  price: “$10”;
  availability: false
  • Arrays: Allow you to assign multiple elements to a variable.

var frameworks = [“React”, “Vue”, “Angular”];

We also have Functions, Loops, and Conditional Statements. Let’s have a look at an example using some of these concepts:

function myComparison(x, y) {
   if (x > y) {
       return -1;
   } else if (x < y) {
       return 1;
   return 0;

Knowing these foundational blocks allows developers to build the web of today, the web we all know and love.

What Is WebAssembly?

WebAssembly Logo

WASM is a low-level, bytecode, and assembly-like language designed to run natively on the web. WebAssembly's initial version was launched in 2017 as an open standard created and maintained by W3C, Mozilla, Microsoft, Google, and Apple. It is also widely supported by major browsers like Chrome, Edge, Firefox, Safari, and Opera.

You can get a list of the current WASM features that each browser natively supports on this page.

WebAssembly (WASM) was designed with a single aim in mind: to execute efficient modern browser-based apps at high-performance levels. What’s more, in WebAssembly, this should be accomplished without jeopardizing compatibility or security.

A fantastic feature of WASM is that it allows source code written in other programming languages like C/C++, C#, and Rust to be compiled and run on the web. Despite its benefits, WASM hasn’t enjoyed widespread adoption with developers, with only 10% of developers saying they’ve used it in a recent survey.

The Anatomy of WebAssembly

Like all other programming languages, WebAssembly is built on a couple of fundamental concepts. Let’s have a look at some of these concepts:

  • Values: These are value types provided by WebAssembly. There are currently four listed types, including integers and more sophisticated floating-point numbers. These numbers can represent booleans and memory locations.

  • Module: It’s a piece of executable machine code compiled by the browser from WebAssembly binary. It has the .wasm file extension and may be imported and exported by the host environment in which it was embedded.

  • Table: It is an array comprising the values of particular items. It includes pointers to function memory locations.

  • Functions: Organized blocks of code that accept and return sets of values as parameters and outputs, respectively.

All these concepts make up the WebAssembly code structure. This code can be in a text and binary format. To compile WASM code, the browser’s Virtual Machine goes through three processes:

  1. Decoding the modules

  2. Compile, optimize, and validate the code against predefined criteria

  3. Executing the compiled code

Here’s an approximation of how a WebAssembly hypothetical app would spend its time, courtesy of Lin Clark from Code Cartoons.

This diagram shows where the WASM engine spends its time for a hypothetical app, but keep in mind that this number may vary. The time that the WASM engine spends doing any of these tasks depends on the kind of work WebAssembly is doing on the page. But we can use this diagram to build a mental model.

WebAssembly performance compared to a typical web application

Let’s take a look at a sample WebAssembly module in WASM Text Format (WAT).

   (func $addNums (param i32 i32)
      (result i32)
         (get_local 0)
         (get_local 1))
   (export “addNums” (func $addTwo))

The code snippet above contains a module in which a function is defined. The process accepts values as parameters and returns the resulting values. The function is then exported and can then be invoked in the browser.

Why All The Hype Around WebAssembly?

The launch of WebAssembly has generated a lot of buzz, owing to the vast possibilities it opens up for developers.

To begin with, developers can make a plethora of native applications accessible via the browser without exhausting, restructuring, or jeopardizing performance.

Furthermore, WASM provides a secure approach to deploy innovation in the browser runtime quickly. While Javascript has been helpful as a dynamic language, its security has long been a source of worry.

WASM developers can use Sandboxes as security measures to execute secure and high-performance applications. Many early adopters feel this will allow JavaScript to return to its original goal as a scripting language that powers browser interactivity.

However, it's worth noting that while WebAssembly was designed to take over the computationally intensive responsibilities of JavaScript, it was never intended to be a rival that would snuff out JavaScript's dominant position in the browser ecosystem.

Indeed, the official WASM documentation emphasizes that WebAssembly was created to supplement JavaScript. Furthermore, WASM presently requires HTML and JS to show generated code results on the web successfully.

JavaScript vs. WebAssembly: Pros and Cons


Many websites, including eCommerce stores, adopt JavaScript as their language of choice. Let’s examine some of the reasons why this is so:


  • Flexibility: The biggest reason for Javascript’s popularity is its versatility. Developers can use JavaScript for a wide range of capabilities. Take notable e-commerce sites like eBay and Walmart, for example. They can use Javascript libraries like React to build beautiful storefronts while using Node.js to power their server-side functionalities.

  • Simplicity: Javascript has a human-readable syntax that makes it simple to learn. In fact, JS has emerged as the preferred programming language for beginners, and this extensive appeal has resulted in a thriving ecosystem that makes recruiting developers simple.

  • Relatively Fast: Since Javascript is an interpreted language, it can be quite fast, producing optimal speed when used for specific web tasks. This vastly increases developers’ productivity which has also contributed to its widespread usage and adoption.


  • Client-Side Security: The use of scripts adds additional processes that malicious attackers can abuse. According to recent research, 97 percent of the websites evaluated used one or more insecure JavaScript functions. The proliferation of unaudited third-party libraries in the JS ecosystem has increased the frequency of these attacks. Owners of critical systems, such as payment checkouts, should not rely solely on client-side validation checks to secure their online applications.

  • Inconsistent Browser Support: Despite efforts to standardize JS features across the board, developers face cross-browser compatibility difficulties, making building unified application UI hard.

  • Inefficient Debugging Support: Since JavaScript is an interpreted language that does not require a compiler, it is easy to deploy applications without noticing critical vulnerabilities. Due to its asynchronous nature, debugging the root causes of errors can be complex. Extensive tools like linters and other IDE plugins make it possible to write error-free JS code.

When Is JavaScript A Good Idea?

JavaScript was primarily designed for adding interactivity to web pages and applications. That said, developers can use JavaScript for several purposes because of its dynamic nature, from embedded systems to desktop applications. Project owners might, however, experience significant performance issues as the project becomes more complex. As such, it is essential to use JavaScript responsibly.

Here are some common use cases for JavaScript:

JavaScript Use Cases

  • Mobile games

  • Developing mobile applications

  • Creating User interfaces for Web Applications

  • Powering server-side applications using Node.js



  • Fast performance: WebAssembly was designed to conduct high-performance computations at near-native speeds. Unlike Javascript, WASM is statically typed, which means code optimization occurs far earlier in the compilation process before the code reaches the browser. Its binary files are considerably smaller than JavaScript's, resulting in significantly faster loading times.

  • Cross-Platform Support: As stated earlier, one of the biggest drivers for WASM adoption is that developers can write code for the web in languages other than JavaScript and port existing applications over the web. Portability is a prominent feature of WebAssembly from the beginning, and this makes it worthwhile outside the browser powering efficient and performant applications on various operating systems.

  • Top-Notch Security: WebAssembly was built with security in mind. Its goal is to protect users from potential web insecurities while empowering developers to produce secure applications. WebAssembly provides a secure application experience by isolating module execution in a sandboxed environment while enforcing known browser security policies.


  • Early Stage: WASM is still in its early stages of development, and it will take some time before it builds the rich environment that JS had 20 years to create. WebAssembly, for example, currently lacks document object model (DOM) and garbage collection features, and it still relies on JavaScript for full platform access.

  • Language Complexity: One of the biggest drivers of JavaScript adoption among beginners who want to make an immediate impact is a high-level language like Python. WASM is a low-level language making it difficult to learn, which may prevent it from being as popular as JavaScript.

  • Imperfect Security: Although WASM was built with security in mind, some features make it useful for malicious attackers. Already researchers have discovered that about 50% of websites that use WASM use it to propagate security vulnerabilities. Because WASM is compiled code, browsers might find detecting security issues in the obfuscated format challenging. Furthermore, while the sandbox feature was designed to contain exploits, recent findings have proven this to be not entirely accurate. These concerns might be linked to the teething problems of a new language. WebAssembly may prove to be the solution that finally minimizes browser-based attacks as more features are developed.

When Should You Use WebAssembly?

Given the benefits of WebAssembly, developers should use it when creating computing-intensive apps. They can even use more established low-level languages recognized for their performance capabilities and then compile the code to the web using WASM. There are other recommended use cases such as:

WebAssembly Use Cases

  • Hybrid-platform apps

  • Developing CPU intensive Games

  • High-performance scientific simulations

  • Music streaming and Image caching applications

  • Developing applications that encrypt sensitive data

WebAssembly vs. JavaScript: Comparison

  JavaScript WebAssembly
Loading Time Javascript can be incredibly fast for smaller tasks. WASM is perfect for heavy computation applications. It also has smaller files resulting in faster loading times.
Execution Speed Because JS is an interpreted language, it might take a while before the browser fully understands what it’s about to execute. WASM’s strongly typed code is already optimized before getting to the browser, making execution quite faster.
Garbage Collection JavaScript has an extensive garbage collection process used for memory management. WASM relies on JS for garbage collection.
Memory Usage Again, JS garbage collection automatically takes care of memory usage. Memory usage is quite complex in WASM. Developers get linear memory allocations which they have to manage manually.
Platform API Access Javascript has extensive platform API access. WASM doesn’t have direct API access. All DOM manipulation has to be done via JS.
Debugging As an interpreted language, debugging happens during runtime, which may appear faster but may allow errors and vulnerabilities to slip through the cracks. As a compiled language, debugging occurs before compilation, meaning the code doesn't compile if errors are found.
Multithreading As a single-threaded language, Javascript relies on web workers for multiple executions. As of now, there’s no Multithreading support for WASM. You can, however, use other low-level languages with Multithreading capabilities.
Portability Developers can use JavaScript for multiple use cases and across various platforms. WASM was built with portability in mind. Developers can use it in and outside browser platforms.

Which One Should You Learn?

WASM was designed to complement JavaScript’s capabilities. As a result, your goal should influence your decision to study one or the other.

Are you a beginner who wants to create a beautiful user interface without much complexity? Then, learning Javascript should be a better option for you. If you intend to run secure and computationally intensive apps without having to worry about performance concerns as you scale, learning WASM could be the best option for you.

Other factors that should influence your decision are extensive documentation and the existence of productivity-enhancing tools.

In the end, pick the language that you feel will help you achieve your goals, and don’t learn something only because it’s cool or new.

Will WebAssembly (WASM) Replace JavaScript? Not Really

While JavaScript has certain fundamental flaws that WASM was designed to fix, WebAssembly will not be replacing JavaScript in the near future. Furthermore, WASM still has a long way to go before it can be considered a credible option for disruption.

A more reasonable viewpoint would be that both languages collaborate to enhance and advance the cause of browser-based applications. While developers seek fast and predictable performance for large projects, WASM will be preferred, while JavaScript will remain the de facto language for interactive mobile and web apps.

About the author

Diego Salinas Gardón
Content Strategist and Jamstack Community Creator

Diego is a content strategist and Jamstack Community Creator. He is interested in Futures Thinking, low-code development, and the democratization of technology for non-English speakers. He spends his free time writing non-fiction and poetry.
Connect with him on LinkedIn.

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