Ant: A Lightweight JavaScript Runtime Built from Scratch

The modern JavaScript ecosystem is dominated by heavyweights like V8, SpiderMonkey, and JavaScriptCore. While these engines provide immense power and optimization, they come with a significant cost: binary size. For developers building CLI tools or lightweight Docker containers, dragging along 50MB to 100MB of runtime overhead is often an unacceptable trade-off.

Enter Ant, a from-scratch JavaScript runtime designed specifically to prioritize a minimal footprint without sacrificing the speed required for modern serverless and edge applications. By eschewing the traditional approach of wrapping existing large-scale engines, Ant offers a glimpse into how specialized runtimes can optimize for cold-start performance and distribution size.

The Architecture of Ant

Unlike many alternative runtimes that act as wrappers around V8 or Bun, Ant is powered by its own hand-written engine, referred to as "Ant Silver." This architectural decision is the primary driver behind its remarkably small size. Currently, the Ant binary sits at approximately 9MB, which can be further reduced to 6.5MB when compiled with the -Os optimization flag.

Performance and Cold Starts

One of the most critical metrics for modern cloud infrastructure is the "cold start"—the time it takes for a runtime to initialize and execute the first request. In benchmarks using Hono (a small, fast web framework), Ant demonstrates significant advantages over its larger competitors on M4 Pro hardware:

• Ant: ~5ms cold start
• Bun: ~2.4x slower than Ant
• Node.js: ~5.8x slower than Ant

While the author notes that Ant is performant enough to compete with V8 in specific shapes and scenarios, it is optimized primarily for these rapid initialization cycles rather than raw, long-running throughput.

Compatibility and Standards

Building a runtime from scratch poses a massive challenge in terms of language specification compliance. Ant targets the WinterCG Minimum Common API, ensuring it can run code designed for the edge and serverless environments.

In terms of language compliance, Ant has achieved the following milestones:

• javascript-zoo compat-table: 100% pass rate.
• test262: Approximately 64% completion.

To handle execution efficiency, Ant is implementing a JIT (Just-In-Time) compiler, which currently utilizes a fork of MIR (Mid-level Intermediate Representation) as its backend. This indicates a roadmap toward higher execution speeds as the JIT matures.

Industry Implications: Serverless and Edge Computing

The emergence of a runtime like Ant sparks important discussions about the future of serverless computing. Traditional AWS Lambda functions often struggle with cold start latency, leading Cloudflare to implement V8 isolates as a workaround. However, isolates often lack a full Node.js environment.

As noted by community observers, a runtime that is both small and fast could potentially eliminate the environment-specific trade-offs currently faced by developers:

"Imagine this in a serverless environment... Maybe this could make it so the code always runs quickly regardless of the env it's in."

Challenges and Alternatives

While Ant represents a breakthrough in size, the community continues to debate the best path toward high-performance JavaScript. Some suggest that the ultimate goal for speed and size should be a compiler that translates JavaScript directly into LLVM, effectively turning the dynamic language into a statically compiled binary.

However, Ant's approach provides an immediate, practical solution for those who need a runtime that is small enough to be embedded directly into CLIs or minimal containers without the bloat of a full-scale browser engine.