Will WebAssembly replace JavaScript?

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One of the most powerful innovations in recent past decades for the internet, WebAssembly is an open standard that defines a portable binary-code format for executable programs. It is fast and portable in the real sense. What makes it really useful is the fact that most of the programming languages including Rust and C++ have wasm as the compile target. Rust is a very powerful language because of its efficient memory management. More than 9 companies including Dropbox, Coursera, Figma, npm, Microsoft, Cloudflare, Facebook, Amazon and Discord use Rust for one or the other things. Seeing such great benefits of WebAssembly, We wonder “Will WebAssembly replace JavaScript?”

This is one of the most frequently asked questions nowadays. So let’s do a quick comparison to see if WebAssembly can replace JS or not.

In this blog, we will try to find when JavaScript performs better than wasm and when wasm is better than JS. Also, we will see how wasm works and why is it a good choice for web deployment.

An Alternative for JS

We’ve been using JavaScript as the only programming language that is native to web browsers and then we saw WebAssembly coming. But what actually WebAssembly is. Let’s look at the definition of wasm.

WebAssembly, generally called wasm, is a compact, fast and portable code that can run on most browsers. WebAssembly is a binary instruction format similar to byte code in java. This code can not be understood by us but by a stack-based virtual machine. A stack-based virtual machine is a virtual machine that considers the operands of all the instructions as they are on a stack.

We generally don’t write code in wasm. Wasm is a compilation target for many programming languages. Many languages compile their code to wasm, making it easier to transfer on the web for deployment purposes.

One more thing, wasm is neither an assembly language nor it’s not built for a specific machine.

What it does is compile higher-level languages and then run those web apps in the browser a lot faster than JavaScript.

Some Differences

First of all, we see some of the strengths of JavaScripts then we will see what WebAssembly can do. So that we get a good insight into their powers.

JavaScript is dynamically typed,i.e., the type is associated with run-time values, and not named variables/fields/etc. JavaScript is highly flexible as we all know. The code is JS is a human-readable code. 

On the other hand, WebAssembly is amazingly fast. It is delivered in a small-sized binary format which actually makes it fast to transfer. It is strongly typed.

Working of Wasm

Let us see that how to use wasm and its working.

First, you write the code for your web app in any language namely Rust, C++, etc. Then you compile it into WebAssembly bytecode also known as the wasm file. Then, this wasm file is run in the web browser, where it turns into native machine code and is executed. And it gets loaded, parsed, and executed a lot faster as compared to JavaScript.

The binaries are lightweight and faster to textual JS and thus faster to transfer and execute.

Performance Comparison

We have till now seen that WebAssembly is faster than JS. Let us dig some more deep and see the performance difference between the two.

1. WebAssembly’s binaries are faster to download

JS would need to parse, compile and then optimize the code before executing it which takes longer than the fast binaries WebAssembly has.

It is easy to write code in JS and does not get compiled ahead, since it is a dynamically typed language.

JavaScript still needs more time to do all the needed work before executing the code.

2. WebAssembly manages memory manually

In WebAssembly, there is no garbage pile-up to impact performance.

3. WebAssembly reduces the initial load time

Since wasm is statically typed, it does not need to infer types during the run time. The main reasons that make the initial load time lesser are –

  • It has a binary format
  • It’s statically typed 
  • It performs its optimization task in advance while compiling the source code

JS on the other hand does a task to convert the text into a data structure called Abstract Syntax Tree and then convert the Syntax tree to a binary format.

Wasm is threefold better than JS in load time.

4. JavaScript often performs better during execution

Ok, this looks somewhat contradicting to what we have been discussing before. But here we are talking about execution after the optimization of both the codes. Once fully optimized, WebAssembly is slower than JS when executing code in the browser.


Now it’s time for the most controversial question. Will WASM replace JS in near future?

Actually, I don’t think so because JS is still a very convenient choice for many users to perform many tasks. It will be hard to believe that WASM can do all the tasks JS is capable of doing now.

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