Drop the bundled shim (#216)

* Drop the bundled shim It's no longer needed with full support for import maps in all modern browsers. * More shim docs
rails · Jan 1, 2024 · b372f2e · lafeber · Jan 19, 2024 · b372f2e
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diff --git a/README.md b/README.md
@@ -4,7 +4,7 @@
 
 With this approach you'll ship many small JavaScript files instead of one big JavaScript file. Thanks to HTTP/2 that no longer carries a material performance penalty during the initial transport, and in fact offers substantial benefits over the long run due to better caching dynamics. Whereas before any change to any JavaScript file included in your big bundle would invalidate the cache for the whole bundle, now only the cache for that single file is invalidated.
 
-There's [native support for import maps in Chrome/Edge 89+/Firefox 108+](https://caniuse.com/?search=importmap), and [a shim available](https://github.com/guybedford/es-module-shims) for any browser with basic ESM support. So your app will be able to work with all the evergreen browsers.
+[Import maps are supported natively in all major, modern browsers](https://caniuse.com/?search=importmap). If you need to work with legacy browsers without native support, you can explore using [the shim available](https://github.com/guybedford/es-module-shims).
 
 
 ## Installation
@@ -57,7 +57,7 @@ import React from "react"
 
 The import map is setup through `Rails.application.importmap` via the configuration in `config/importmap.rb`. This file is automatically reloaded in development upon changes, but note that you must restart the server if you remove pins and need them gone from the rendered importmap or list of preloads.
 
-This import map is inlined in the `<head>` of your application layout using `<%= javascript_importmap_tags %>`, which will setup the JSON configuration inside a `<script type="importmap">` tag. After that, the [es-module-shim](https://github.com/guybedford/es-module-shims) is loaded, and then finally the application entrypoint is imported via `<script type="module">import "application"</script>`. That logical entrypoint, `application`, is mapped in the importmap script tag to the file `app/javascript/application.js`.
+This import map is inlined in the `<head>` of your application layout using `<%= javascript_importmap_tags %>`, which will setup the JSON configuration inside a `<script type="importmap">` tag. Then the application entrypoint is imported via `<script type="module">import "application"</script>`. That logical entrypoint, `application`, is mapped in the importmap script tag to the file `app/javascript/application.js`.
 
 It's in `app/javascript/application.js` you setup your application by importing any of the modules that have been defined in the import map. You can use the full ESM functionality of importing any particular export of the modules or everything.
 
@@ -309,16 +309,6 @@ module MyEngine
 end
 ```
 
-## Expected errors from using the es-module-shim
-
-While import maps are native in Chrome, Edge, and Firefox, they need a shim in other browsers that'll produce a JavaScript console error like `TypeError: Module specifier, 'application' does not start with "/", "./", or "../".`. This error is normal and does not have any user-facing consequences.
-
-In Firefox. when opening the browser console, the asm.js module lexer build will run in unoptimized mode due to the debugger attaching. This gives a warning message `"asm.js type error: Disabled because no suitable wasm compiler is available"` which is as expected. When the console is closed again, the asm.js optimizations are fully applied, and this can even be verified with the console open by disabling the debugger in `about:config` and reloading the page.
-
-## Turning off the shim
-
-Under certain circumstances, like running system tests using chromedriver under CI (which may be resource constrained and trigger errors in certain cases), you may want to explicitly turn off including the shim. You can do this by calling the bulk tag helper with `javascript_importmap_tags("application", shim: false)`. Thus you can pass in something like `shim: !ENV["CI"]`. If you want, and are sure you're not doing any full-page caching, you can also connect this directive to a user agent check (using a gem like `useragent`) to check whether the browser is chrome/edge 89+/firefox 108+. But you really shouldn't have to, as the shim is designed to gracefully work with natively compatible drivers.
-
 ## Checking for outdated or vulnerable packages
 
 Importmap for Rails provides two commands to check your pinned packages: