feat(top-level-function): support function expression (#37)

Author: ntnyq

src/rules/top-level-function.md

@@ -1,6 +1,6 @@
 # top-level-function
 
-Enforce top-level function to be declared using `function` instead of arrow function. With auto-fix.
+Enforce top-level function to be declared using `function` instead of arrow function or function expression. With auto-fix.
 
 ## Rule Details
 
@@ -14,6 +14,16 @@ export const square = (a: number, b: number): number => {
 }
 ```
 
+<!-- eslint-skip -->
+```ts
+// 👎 bad
+export const square = function (a: number, b: number): number {
+  const a2 = a * a
+  const b2 = b * b
+  return a2 + b2 + 2 * a * b
+}
+```
+
 <!-- eslint-skip -->
 ```js
 // 👍 good

src/rules/top-level-function.test.ts

@@ -48,6 +48,30 @@ const invalids = [
     'export const foo = async () => \n({})',
     'export async function foo () {\n  return {}\n}',
   ],
+  [
+    'const foo = function () {}',
+    'function foo () {}',
+  ],
+  [
+    'const foo = function (as: string, bar: number) { return as + bar }',
+    'function foo (as: string, bar: number) { return as + bar }',
+  ],
+  [
+    'const foo = function <K, T extends Boolean>(as: string, bar: number): Omit<T, K> { return as + bar }',
+    'function foo <K, T extends Boolean>(as: string, bar: number): Omit<T, K> { return as + bar }',
+  ],
+  [
+    'export const foo = function () {}',
+    'export function foo () {}',
+  ],
+  [
+    'export const foo = function () { \nreturn {} }',
+    'export function foo () { \nreturn {} }',
+  ],
+  [
+    'export const foo = async function () { \nreturn {}\n }',
+    'export async function foo () { \nreturn {}\n }',
+  ],
 ]
 
 run({

src/rules/top-level-function.ts

@@ -33,8 +33,12 @@ export default createEslintRule<Options, MessageIds>({
 
         const declaration = node.declarations[0]
 
-        if (declaration.init?.type !== 'ArrowFunctionExpression')
+        if (
+          declaration.init?.type !== 'ArrowFunctionExpression'
+          && declaration.init?.type !== 'FunctionExpression'
+        ) {
           return
+        }
         if (declaration.id?.type !== 'Identifier')
           return
         if (declaration.id.typeAnnotation)
@@ -46,7 +50,7 @@ export default createEslintRule<Options, MessageIds>({
           return
         }
 
-        const arrowFn = declaration.init
+        const fnExpression = declaration.init
         const body = declaration.init.body
         const id = declaration.id
 
@@ -60,19 +64,19 @@ export default createEslintRule<Options, MessageIds>({
           fix(fixer) {
             const code = context.getSourceCode().text
             const textName = code.slice(id.range[0], id.range[1])
-            const textArgs = arrowFn.params.length
-              ? code.slice(arrowFn.params[0].range[0], arrowFn.params[arrowFn.params.length - 1].range[1])
+            const textArgs = fnExpression.params.length
+              ? code.slice(fnExpression.params[0].range[0], fnExpression.params[fnExpression.params.length - 1].range[1])
               : ''
             const textBody = body.type === 'BlockStatement'
               ? code.slice(body.range[0], body.range[1])
               : `{\n  return ${code.slice(body.range[0], body.range[1])}\n}`
-            const textGeneric = arrowFn.typeParameters
-              ? code.slice(arrowFn.typeParameters.range[0], arrowFn.typeParameters.range[1])
+            const textGeneric = fnExpression.typeParameters
+              ? code.slice(fnExpression.typeParameters.range[0], fnExpression.typeParameters.range[1])
               : ''
-            const textTypeReturn = arrowFn.returnType
-              ? code.slice(arrowFn.returnType.range[0], arrowFn.returnType.range[1])
+            const textTypeReturn = fnExpression.returnType
+              ? code.slice(fnExpression.returnType.range[0], fnExpression.returnType.range[1])
               : ''
-            const textAsync = arrowFn.async ? 'async ' : ''
+            const textAsync = fnExpression.async ? 'async ' : ''
 
             const final = `${textAsync}function ${textName} ${textGeneric}(${textArgs})${textTypeReturn} ${textBody}`
             // console.log({