Add no-class-static-blocks rule

README.md

@@ -1,20 +1,27 @@
 # eslint-plugin-escompat
 
-This plugin will report eslint errors for code which - if left untranspiled - will not work in some browsers.
+This plugin will report eslint errors for code which - if left untranspiled -
+will not work in some browsers.
 
-This is useful if you intend to ship code without first using a transpiler, such as [Babel](https://babeljs.io).
+This is useful if you intend to ship code without first using a transpiler, such
+as [Babel](https://babeljs.io).
 
-This _won't_ lint for features that can be polyfilled. For that you can use [eslint-plugin-compat][epc].
+This _won't_ lint for features that can be polyfilled. For that you can use
+[eslint-plugin-compat][epc].
 
 ## Installation
 
 ```bash
 npm install --save-dev eslint-plugin-escompat
 ```
 
-Add `"escompat"` to `.eslintrc` `"plugins"` section, add `"browser": true` to `"env"`, then configure the individual `"escompat/*"` rules.
+Add `"escompat"` to `.eslintrc` `"plugins"` section, add `"browser": true` to
+`"env"`, then configure the individual `"escompat/*"` rules.
+
+Alternatively, you can use the `recommended` configuration which will do this
+for you, with the `"escompat/*"` rules reporting errors (as in the snippet
+above).
 
-Alternatively, you can use the `recommended` configuration which will do this for you, with the `"escompat/*"` rules reporting errors (as in the snippet above).
 ```js
 // .eslintrc
 {
@@ -24,7 +31,11 @@ Alternatively, you can use the `recommended` configuration which will do this fo
 
 ### TypeScript Users
 
-Aside from the `recommended` config, there are also multiple `typescript` configs which can be used if you're using TypeScript. The TypeScript configs only enable some of the rules, avoiding enabling rules for which `typescript` safely transpiles down to a more compatible syntax. Extend the typescript config that matches your `tsconfig.json` `target` value.
+Aside from the `recommended` config, there are also multiple `typescript`
+configs which can be used if you're using TypeScript. The TypeScript configs
+only enable some of the rules, avoiding enabling rules for which `typescript`
+safely transpiles down to a more compatible syntax. Extend the typescript config
+that matches your `tsconfig.json` `target` value.
 
 ```js
 // .eslintrc
@@ -37,11 +48,11 @@ Aside from the `recommended` config, there are also multiple `typescript` config
 
 `eslint-plugin-escompat` uses the `browserslist` configuration in `package.json`
 
-If you have a browserlist, is is safe to enable all of these rules - as any
-that do not coincide with your chosen browsers will be turned off
-automatically.
+If you have a browserlist, is is safe to enable all of these rules - as any that
+do not coincide with your chosen browsers will be turned off automatically.
 
-See [browserslist/browserslist](https://github.com/browserslist/browserslist) for configuration. Here's some examples:
+See [browserslist/browserslist](https://github.com/browserslist/browserslist)
+for configuration. Here's some examples:
 
 ```js
 // Simple configuration (package.json)
@@ -62,33 +73,37 @@ See [browserslist/browserslist](https://github.com/browserslist/browserslist) fo
 }
 ```
 
-:bulb: You can also define browsers in a [separate browserslist file](https://github.com/browserslist/browserslist#config-file)
+:bulb: You can also define browsers in a
+[separate browserslist file](https://github.com/browserslist/browserslist#config-file)
 
 ## Rules
 
- - [no-async-generator](./docs/no-async-generator.md)
- - [no-async-iteration](./docs/no-async-iteration.md)
- - [no-bigint](./docs/no-bigint.md)
- - [no-bind-operator](./docs/no-bind-operator.md)
- - [no-computed-public-class-fields](./docs/no-computed-public-class-fields.md)
- - [no-do-expression](./docs/no-do-expression.md)
- - [no-dynamic-imports](./docs/no-dynamic-imports.md)
- - [no-edge-destructure-bug](./docs/no-edge-destructure-bug.md)
- - [no-exponentiation-operator](./docs/no-exponentiation-operator.md)
- - [no-nullish-coalescing](./docs/no-nullish-coalescing.md)
- - [no-numeric-separators](./docs/no-numeric-separators.md)
- - [no-object-rest-spread](./docs/no-object-rest-spread.md)
- - [no-optional-catch](./docs/no-optional-catch.md)
- - [no-optional-chaining](./docs/no-optional-chaining.md)
- - [no-pipeline-operator](./docs/no-pipeline-operator.md)
- - [no-private-class-fields](./docs/no-private-class-fields.md)
- - [no-public-instance-class-fields](./docs/no-public-instance-class-fields.md)
- - [no-public-static-class-fields](./docs/no-public-static-class-fields.md)
- - [no-regexp-lookbehind](./docs/no-regexp-lookbehind.md)
- - [no-regexp-named-group](./docs/no-regexp-named-group.md)
- - [no-regexp-s-flag](./docs/no-regexp-s-flag.md)
+- [no-async-generator](./docs/no-async-generator.md)
+- [no-async-iteration](./docs/no-async-iteration.md)
+- [no-bigint](./docs/no-bigint.md)
+- [no-bind-operator](./docs/no-bind-operator.md)
+- [no-class-static-blocks](./docs/no-class-static-blocks.md)
+- [no-computed-public-class-fields](./docs/no-computed-public-class-fields.md)
+- [no-do-expression](./docs/no-do-expression.md)
+- [no-dynamic-imports](./docs/no-dynamic-imports.md)
+- [no-edge-destructure-bug](./docs/no-edge-destructure-bug.md)
+- [no-exponentiation-operator](./docs/no-exponentiation-operator.md)
+- [no-nullish-coalescing](./docs/no-nullish-coalescing.md)
+- [no-numeric-separators](./docs/no-numeric-separators.md)
+- [no-object-rest-spread](./docs/no-object-rest-spread.md)
+- [no-optional-catch](./docs/no-optional-catch.md)
+- [no-optional-chaining](./docs/no-optional-chaining.md)
+- [no-pipeline-operator](./docs/no-pipeline-operator.md)
+- [no-private-class-fields](./docs/no-private-class-fields.md)
+- [no-public-instance-class-fields](./docs/no-public-instance-class-fields.md)
+- [no-public-static-class-fields](./docs/no-public-static-class-fields.md)
+- [no-regexp-lookbehind](./docs/no-regexp-lookbehind.md)
+- [no-regexp-named-group](./docs/no-regexp-named-group.md)
+- [no-regexp-s-flag](./docs/no-regexp-s-flag.md)
 
 ## Inspiration
-This project was largely inspired by the great [eslint-plugin-compat][epc] library.
+
+This project was largely inspired by the great [eslint-plugin-compat][epc]
+library.
 
 [epc]: https://github.com/amilajack/eslint-plugin-compat

docs/no-class-static-blocks.md

@@ -0,0 +1,47 @@
+# no-class-static-blocks
+
+This prevents the use of Static Blocks within Classes, for example:
+
+```js
+class Foo {
+  static {
+    this.x = 1;
+  }
+}
+```
+
+These will not be allowed because they are not supported in the following
+browsers:
+
+- Edge < 94
+- Safari > 0
+- Firefox < 93
+- Chrome < 94
+
+## What is the Fix?
+
+You can safely use _static fields_, where each property is given the `static`
+keyword:
+
+```js
+class Foo {
+  static x = 1;
+}
+```
+
+If you wish to evaluate a field using logic, you can do so with an IIFE:
+
+```js
+class Foo {
+  static x = (() => {
+    if (env == "DEBUG") {
+      return 4;
+    }
+    return Math.random();
+  })();
+}
+```
+
+This can be safely disabled if you intend to compile code with the
+`@babel/plugin-proposal-class-static-block` Babel plugin, or
+`@babel/preset-env`.