diff --git a/docs/README_js.md b/docs/README_js.md
index d80e02c..937c0e5 100644
--- a/docs/README_js.md
+++ b/docs/README_js.md
@@ -14,14 +14,14 @@ An API for MIME type information.
 - Full TS support
 
 
-> **Important**
-> `mime@4` is currently in **beta**. Changes include:
-> * ESM module support is required.  See the [ESM Module FAQ](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c).
-> * [ES2020](https://caniuse.com/?search=es2020) support is required
-> * Typescript types are built-in
->
-> To install:  ` npm install mime@beta`
-## Install
+> [Note!]
+> `mime@4` has now `latest`.  If you're upgrading from `mime@3`, note the following:
+> * `mime@4` is API-compatible with `mime@3`, with one exception: `mime.define()` cannot be called on the default `mime` object.
+> * ESM module support is required.   [ESM Module FAQ](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c).
+> * Requires an [ES2020](https://caniuse.com/?search=es2020) or newer runtime
+> * Built-in Typescript types (`@types/mime` no longer needed)
+
+## Installation
 
 ```bash
 npm install mime
@@ -82,7 +82,7 @@ mime.getExtension('text/html; charset=utf8'); // RESULT
 
 ### `mime.getAllExtensions(type)`
 
-> **Note**
+> [!Note]
 > New in `mime@4`
 
 Get all file extensions for the given mime type.
@@ -93,7 +93,7 @@ mime.getAllExtensions('text/plain'); // RESULT
 
 ## Custom `Mime` instances
 
-The default objects exported by `mime` are immutable by design.  Mutable versions can be created as follows...
+The default `mime` objects are immutable.  Custom, mutable versions can be created as follows...
 ### new Mime(type map [, type map, ...])
 
 Create a new, custom mime instance.  For example, to create a mutable version of the default `mime` instance:
@@ -111,7 +111,7 @@ Each argument is passed to the `define()` method, below. For example `new Mime(s
 
 ### `mime.define(type map [, force = false])`
 
-> **Note**
+> [!Note]
 > Only available on custom `Mime` instances
 
 Define MIME type -> extensions.
@@ -129,10 +129,14 @@ mime.getExtension('text/x-abc'); // RESULT
 
 ### Extension -> type
 
-    $ mime scripts/jquery.js
-    application/javascript
+```bash
+$ mime scripts/jquery.js
+application/javascript
+```
 
 ### Type -> extension
 
-    $ npx mime -r image/jpeg
-    jpeg
+```bash
+$ mime -r image/jpeg
+jpeg
+```
\ No newline at end of file
diff --git a/src/Mime.ts b/src/Mime.ts
index f81268c..a28323b 100644
--- a/src/Mime.ts
+++ b/src/Mime.ts
@@ -116,7 +116,7 @@ export default class Mime {
 
   _freeze() {
     this.define = () => {
-      throw new Error('define() not allowed for built-in Mime objects.');
+      throw new Error('define() not allowed for built-in Mime objects. See https://github.com/broofa/mime/blob/main/README.md#custom-mime-instances');
     };
 
     Object.freeze(this);