What Are the Differences Between WebAssembly and the JVM?

At their core, both the JVM and WebAssembly were designed to run compiled code just about anywhere—for the JVM, this meant machines with different operating systems or CPU architectures, something unprecedented for its time, and for WebAssembly, this meant any web browser on any computer anywhere, for the rest of time.

The JVM, introduced in the mid-1990s alongside Java, evolved into a full-fledged platform providing rich runtime support—garbage collection, extensive standard libraries, and tools for managed execution. However, some might say this gives the JVM a considerable amount of bloat: large memory footprints and slower startup times. While extremely powerful, this makes the JVM less suitable for lightweight applications.

In contrast, WebAssembly was designed with the web in mind—specifically for running code inside browsers. As a result, it was architected to prioritize a lightweight runtime and lightning-fast startup times, but without the rich runtime support. Only targeting browsers would make Wasm less portable than Java bytecode, but today, standalone Wasm runtimes can run outside the web, opening new doors for server-side applications, embedded systems, and edge computing. Additionally, some limited additional runtime support is coming to WebAssembly, namely, garbage collection, but we’re unlikely to see the full breadth of runtime support in WebAssembly that the JVM offers.

The JVM only works with its family of languages—Java, Kotlin, Scala, and a few more—all of which are intentionally designed to run atop the JVM. While the Java ecosystem has extensive libraries and frameworks, interoperability only happens between these JVM languages. JVM-based applications can call out to native code, but not without great effort and care.

WebAssembly wasn’t designed to only support one programming language or to favor a certain style of language, whether functional, garbage-collected, or interpreted. Any language—Rust, JavaScript, Python, C++—could be compiled to run on a Wasm runtime. While that doesn’t mean that code from each of these languages would be able to talk to each other right now, through the emerging Component Model standard, developers are able to take multiple Wasm modules written in different languages and connect them seamlessly. Soon, for WebAssembly, linking and interoperability will be a given.

When was the last time you heard that someone embedded the JVM into an application to run plugins or custom logic? Not recently, if ever, was it? While the JVM is powerful, it’s notoriously challenging to embed into other applications. Some high-profile embeddings have happened (like Java applets in browsers) but they have largely fallen off because of their clunkiness or maintainability.

WebAssembly, on the other hand, is designed for embeddability. Embedding a Wasm runtime in an application is often as easy as pulling in a new library. Once that’s done, your application can run Wasm code—this could be to extend a game engine, modify an algorithm, respond to an event, or anything else you could dream up. Wasm provides versatility in embeddability that the JVM isn’t equipped to offer (or wants to offer, for that matter).

This is arguably where WebAssembly shines the brightest. The JVM has its own security model, but it was designed under the assumption that code being executed is trusted. WebAssembly fundamentally rejects that premise—born in the browser, where visiting a website necessarily downloads untrusted code and runs it, Wasm employs a strict deny-by-default sandbox model. It doesn’t grant code access to system resources, memory, or other functionality unless explicitly authorized. This approach inherently minimizes attack surfaces and makes Wasm ideal for environments where untrusted code execution is a concern.

The JVM’s security model is functional, but it just wasn’t designed for the level of security that Wasm offers.

The JVM is a seasoned veteran in the tech world. With decades of history under its belt, it’s backed by tremendous adoption, extensive enterprise tooling, and a community so vast that it feels like an immovable force in software development—we know it’s not going away any time soon. If longevity and proven stability are key for your use cases, the JVM delivers.

WebAssembly, meanwhile, is still the new kid on the block. Despite being younger and just shy of its 10th birthday, the enthusiasm surrounding Wasm is growing at an exponential rate. Though less mature than the JVM today, WebAssembly’s trajectory suggests a bright future.

Both WebAssembly and the JVM are incredible technologies, each excelling in ways that suit their environments and use cases. The JVM thrives in enterprise workflows where full-blown applications and rich runtime capabilities matter. On the other hand, Wasm’s embeddability, lightweight runtime, cross-language compatibility, and unparalleled security make it a compelling choice for plugins and edge computing.

So, which should you choose? If you’re developing standalone applications with robust runtime needs, the JVM remains a practical and time-tested choice. But if you want flexibility across languages or the ability to plug into existing apps with ease, WebAssembly might just tip the scales.