TL;DR
Mozilla has disabled asm.js in Firefox 148 and plans to remove it entirely in a future release. This shift reflects the success of WebAssembly, which has largely replaced asm.js for high-performance web applications.
Mozilla has officially disabled asm.js optimizations in Firefox 148 and announced plans to remove the code entirely in a future release, marking the end of a technology that once enabled near-native performance on the web. NYT and Vaping: How to Lie by Saying Only True Things
Starting with Firefox 148, Mozilla has disabled SpiderMonkey’s asm.js optimizations by default. The company clarified that sites using asm.js will continue to function normally, as it is just a subset of JavaScript that runs through the regular JIT compiler. The planned removal aims to reduce maintenance overhead and security risks associated with supporting deprecated code.
Asm.js was introduced by Mozilla in 2013 as a way to enable high-performance web applications by using a strict, statically-typed subset of JavaScript. It allowed projects like Unity and Unreal Engine to port C/C++ codebases to the web, significantly expanding the capabilities of browser-based gaming and interactive content. The technology was a precursor to WebAssembly, which eventually superseded asm.js due to its superior performance and smaller binary sizes.
Mozilla’s OdinMonkey compiler, responsible for translating asm.js, will be phased out, with the company emphasizing that WebAssembly now provides a more advanced pipeline for high-performance web code. Mozilla encourages developers to migrate existing asm.js content to WebAssembly, citing faster execution and smaller binaries as benefits.
Why It Matters
This development marks the end of an era for web-based high-performance computing. Asm.js played a crucial role in demonstrating that complex, near-native applications could run within standard web browsers, paving the way for WebAssembly’s success. Its removal reflects a mature ecosystem where WebAssembly is now the standard for performance-critical web applications, reducing legacy support burdens and improving security.
For developers and companies relying on asm.js, the transition to WebAssembly is strongly recommended to benefit from better performance and ongoing support. The move also signals a broader shift toward modern web standards that prioritize efficiency and security.
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Background
Asm.js was developed by Mozilla as a response to Google’s Native Client (NaCl) and Portable Native Client (PNaCl), aiming to achieve native-like performance within the browser environment. It was first shipped in Firefox 22 in 2013 and quickly gained adoption in gaming and multimedia projects. The success of asm.js demonstrated that complex, performance-critical applications could run on the web, influencing the development and adoption of WebAssembly, which shipped in Firefox 52 in 2017.
Over the years, WebAssembly has become the preferred technology for high-performance web applications, with broader industry support and more advanced features. Mozilla’s announcement to phase out asm.js aligns with this transition, as the technology’s usage has declined significantly and maintenance costs increase. I Stopped Saying This Popular Cue When I Teach Yoga. Here’s Why.
“Starting with Firefox 148, asm.js optimizations are disabled by default, with plans to remove the code entirely in a future release.”
— Mozilla Developer Blog
“Recompiling to WebAssembly will provide faster execution and smaller binaries, making it the recommended path forward for high-performance web applications.”
— Mozilla developer
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What Remains Unclear
It is not yet clear when exactly Firefox will remove asm.js support entirely, as the timeline depends on future releases. Additionally, some legacy sites may still rely on asm.js, and the impact on those remains to be assessed. Mozilla has not specified whether any fallback or compatibility measures will be provided during the transition.
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What’s Next
Developers are advised to begin migrating their asm.js-based applications to WebAssembly to ensure continued performance benefits. Mozilla will likely announce specific release dates for the complete removal of asm.js support in upcoming Firefox versions. Industry-wide, other browsers are expected to follow Mozilla’s lead, further consolidating WebAssembly as the standard for high-performance web code.
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Key Questions
Why is Mozilla removing asm.js support?
Mozilla is removing asm.js support because WebAssembly now provides a more advanced, efficient, and secure platform for high-performance web applications, making asm.js redundant.
Will websites that use asm.js stop working?
No. Sites using asm.js will continue to run as usual, as the code is just JavaScript recognized by the browser. However, performance benefits will be better if migrated to WebAssembly.
When will asm.js be fully removed from Firefox?
Mozilla has not specified an exact date but plans to remove asm.js entirely in a future Firefox release after the feature has been disabled by default in 148.
Should I start converting my asm.js code to WebAssembly?
Yes. Mozilla recommends migrating to WebAssembly to benefit from faster execution, smaller binaries, and ongoing support.
Source: Hacker News
