Ruby::Box support—is it possible in Ruby WASM? #645

Activity

1. ledsun commented on May 1, 2026

   

   ledsun

   on May 1, 2026

   Contributor

   More actions

   Yes, Ruby::Box can run on ruby.wasm.

   Importantly, to enable Ruby::Box, you must specify RUBY_BOX=1 as an environment variable when starting the Ruby VM. Setting ENV[“RUBY_BOX”] = “1” from within Ruby code is too late.

   For example, this works on Node.js:

   import fs from "fs/promises";
   import { DefaultRubyVM } from "@ruby/wasm-wasi/dist/node";
   
   const binary = await fs.readFile(
     "./node_modules/@ruby/head-wasm-wasi/dist/ruby.wasm",
   );
   const module = await WebAssembly.compile(binary);
   
   const { vm } = await DefaultRubyVM(module, {
     env: {
       RUBY_BOX: "1",
     },
   });
   
   const result = vm.eval(`
     box = Ruby::Box.new
     box.eval <<~RUBY
       X = 123
     RUBY
   
     puts "Ruby::Box.enabled?: #{Ruby::Box.enabled?}"
     puts "box::X: #{box::X}"
   `);

   Example output:

   $ node ruby-box.node.js
   (node:8080) ExperimentalWarning: WASI is an experimental feature and might change at any time
   (Use `node --trace-warnings ...` to show where the warning was created)
   ruby.wasm: warning: Ruby::Box is experimental, and the behavior may change in the future!
   See https://docs.ruby-lang.org/en/master/Ruby/Box.html for known issues, etc.
   Ruby::Box.enabled?: true
   box::X: 123

   The same applies in browsers if you instantiate the VM manually, e.g. by passing env to DefaultRubyVM:

   const { vm } = await DefaultRubyVM(module, {
     env: {
       RUBY_BOX: "1",
     },
   });

   Note

   Currently, browser.script.iife.js does not provide a way to pass environment variables from HTML.

   👍React with 👍1Reacted by Brandon Zylstra

   ❤️React with ❤️1Reacted by Brandon Zylstra

   🚀React with 🚀1Reacted by Brandon Zylstra
2. brandonzylstra commented on May 2, 2026

   

   brandonzylstra

   on May 2, 2026

   ContributorAuthor

   More actions

   Are there any plans to update browser.script.iffe.js to make it easy to pass in custom options?
3. ledsun commented on Aug 16, 2026

   

   ledsun

   on Aug 16, 2026

   Contributor

   More actions

   This is now supported as of ruby.wasm v2.10.0, via #649.

   browser.script.iife.js accepts a data-env attribute containing a JSON object, so Ruby::Box can now be enabled directly from HTML:

   <script
     src="https://cdn.jsdelivr.net/npm/@ruby/4.0-wasm-wasi@2.10.1/dist/browser.script.iife.js"
     data-env='{"RUBY_BOX":"1"}'
   ></script>
   
   <script type="text/ruby">
     box = Ruby::Box.new
     box.eval("X = 123")
   
     puts "Ruby::Box.enabled?: #{Ruby::Box.enabled?}"
     puts "box::X: #{box::X}"
   </script>

   The values in data-env must be strings.

   I believe this addresses your original question and the subsequent requests.
   Please let me know if there’s anything else you need. Otherwise, I think it’s fine to close this issue.
4. brandonzylstra commented on Aug 17, 2026

   

   brandonzylstra

   on Aug 17, 2026

   ContributorAuthor

   More actions

   Thanks I'll plan to try that and report back. (I previously just altered the JS file, which has worked out well.)