Cross-Runtime JavaScript: Navigating Runtime Differences

by Hexagon, 2 minutes read javascript typescript cross-runtime nodejs deno bun

Discover strategies for handling runtime differences and ensuring smooth cross-platform execution of your JavaScript code.



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Our cross-runtime JavaScript journey has provided a streamlined development setup built upon modern runtimes like Deno and Bun. While the landscape is constantly evolving, one challenge remains: subtle differences between these runtimes. Let's explore how to navigate them.

The Challenge of Runtime Variations

Even with the best intentions, JavaScript runtimes can exhibit variations in their implementations of standard APIs, supported features, and even subtle behavioral quirks. These differences can trip up unsuspecting developers, compromising your code's cross-platform compatibility.

Handling this could be done manually with techniques like:

Feature Detection: Don't assume everything is available everywhere. Proactively check for the feature you need before using it:

if (typeof someFeature !== "undefined") {
  // Use someFeature
} else {
  // Provide a fallback or alternative behavior
}

... or Conditional Import/Execution When differences are substantial, it is possible to create conditional clauses handling each runtime separately:

if (typeof Deno !== "undefined") {
  // Deno-specific code
} else if (typeof Bun !== "undefined") {
  // Bun-specific code
} else {
  // Node.js or browser-specific code
}

However, doing this over and over throughout every project isn't a good practice, and should be avoided.

Existing solutions

The new package registry jsr.io introduces a great standard library, which do cover many scenarios where feature detection, polyfilling or conditional execution would otherwise be needed.

One great example is @std/path, which i use in many of my recent projects. It just works, and are fully cross-runtime, including browsers.

Moving on to more complex scenarios, where @std falls flat, we need other alternatives. Luckily there is great ready made options, such as @cross on jsr.io, which I've made lots of contributions to:

  • @cross/utils - Covering common CLI-program tasks such as ansi formatting, argument parsing, spawning child processes and exiting the current process.

  • @cross/env - Covering getting environment variables, including dotenv and complex scenarios.

  • @cross/runtime - Standardised runtime/os/architecture detection.

  • @cross/fs - Cross-runtime filesystem operations, based on node:fs/promises but exapanded with methods like which(), find(), diskusage() and more.

  • @cross/fs - Cross-runtime filesystem operations, based on node:fs/promises but exapanded with methods like which(), find(), diskusage() and more.

  • @cross/test - Test using the native test runners of Deno, Node and Bun, but with a common interface.

In the next installment, we'll dive into real-world examples of cross-runtime JavaScript applications. Stay tuned!

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