July 27, 2025
The many, many, many JavaScript runtimes of the last decade
This last decade has seen an inundation of new JavaScript runtimes (and engines in equal measure), enabling us to run JavaScript in all manner of contexts with precise fitness for task. Through these, we've seen the language spread to the Cloud, the edge, Smart TVs, mobile devices, and even microcontrollers.
In this article, we'll explore what's driving this diversity, and why no one runtime or engine suffices for all purposes.
Edge computing
The first consumer "edge computing" solution was introduced in 2002 by Akamai, who enabled building on the edge using Java and .NET. But it would be a long time before JavaScript would join those languages – for one thing, JavaScript wouldn't be useful as a server-side language until Node.js emerged in 2009, and for another, Node.js wouldn't be employed in a serverless context until AWS Lambda in 2014. It was only with the announcement of Lambda@Edge (in preview from December 2016; released March 2017) that JavaScript would finally be seen on the edge, again running on Node.js.
But Amazon's monopoly was to be short-lived. For just six months later came the release of Cloudflare Workers, a purpose-built minimal runtime revolving around the Service Worker API. It was devised to open an "entirely new market" to Cloudflare: compute and storage. And this was notably different to Amazon's venture – for the first time in the over twenty years since JavaScript's inception, a company had managed to directly productise a JavaScript runtime.
Cloudflare Workers was a phenomenal success, with billions of tasks run in the half year following its beta release. This scent of opportunity triggered a gold rush. Deno appeared shortly after in 2018 as a challenger to Node.js, and within three years, Deno Land Inc had formed, launching Deno Deploy, an edge network intended to chase after Cloudflare. With an initial treasure chest of $4.9 million and raising a $21 million Series A funding round the year after that, it is clear that Cloudflare weren't the only ones who believed in the value of the niche.
The rush continued in 2022. No sooner had WinterCG been formed to start defining a common ground for all these new JavaScript runtimes popping up than Bun appeared, quickly raising $7 million [archive] to provide serverless hosting, continuous integration, and… edge computing. Wasmer followed suit in 2023, stepping into the Service Workers arena with WinterJS and Wasmer Edge. And not to be outdone, the very next year AWS responded with LLRT, another low-latency runtime just right for the edge (though not yet having an edge worker offering).
For all the overlap in strategy, notable is the variety in engines underpinning all these runtimes. While Deno continues Node.js's tradition of using V8, we see Bun employing JavaScriptCore, WinterJS using SpiderMonkey, LLRT on QuickJS, and Cloudflare Workers on the tailor-made workerd. No longer is the backend solely a stage for Node.js and V8 – it's now fashionable to pick a runtime and engine optimised for the task.
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