typescript-eslint · bradzacher · Feb 29, 2020 · Feb 7, 2020 · Feb 24, 2020 · Feb 27, 2020
diff --git a/packages/eslint-plugin/docs/rules/typedef.md b/packages/eslint-plugin/docs/rules/typedef.md
@@ -37,7 +37,8 @@ This rule has an object option that may receive any of the following as booleans
 - `"objectDestructuring"`
 - `"parameter"`: `true` by default
 - `"propertyDeclaration"`: `true` by default
-- `"variableDeclaration"`
+- `"variableDeclaration"`,
+- `"variableDeclarationIgnoreFunction"`
 
 For example, with the following configuration:
 
@@ -254,6 +255,30 @@ let initialText: string = 'text';
 let delayedText: string;
 ```
 
+### `variableDeclarationIgnoreFunction`
+
+Ignore variable declarations for non-arrow and arrow functions.
+
+Examples of **incorrect** code with `{ "variableDeclaration": true, "variableDeclarationIgnoreFunction": true }`:
+
+```ts
+const text = 'text';
+```
+
+Examples of **correct** code with `{ "variableDeclaration": true, "variableDeclarationIgnoreFunction": true }`:
+
+```ts
+const a = (): void => {};
+const b = function (): void => {};
+const c: () => void = (): void => {};
+
+class Foo {
+  a = (): void => {};
+  b = function (): void => {};
+  c = () => void = (): void => {};
+}
+```
+
 ## When Not To Use It
 
 If you are using stricter TypeScript compiler options, particularly `--noImplicitAny` and/or `--strictPropertyInitialization`, you likely don't need this rule.

diff --git a/packages/eslint-plugin/src/rules/typedef.ts b/packages/eslint-plugin/src/rules/typedef.ts
@@ -12,6 +12,7 @@ const enum OptionKeys {
   Parameter = 'parameter',
   PropertyDeclaration = 'propertyDeclaration',
   VariableDeclaration = 'variableDeclaration',
+  VariableDeclarationIgnoreFunction = 'variableDeclarationIgnoreFunction',
 }
 
 type Options = { [k in OptionKeys]?: boolean };
@@ -41,6 +42,7 @@ export default util.createRule<[Options], MessageIds>({
           [OptionKeys.Parameter]: { type: 'boolean' },
           [OptionKeys.PropertyDeclaration]: { type: 'boolean' },
           [OptionKeys.VariableDeclaration]: { type: 'boolean' },
+          [OptionKeys.VariableDeclarationIgnoreFunction]: { type: 'boolean' },
         },
       },
     ],
@@ -125,6 +127,14 @@ export default util.createRule<[Options], MessageIds>({
       }
     }
 
+    function isVariableDeclarationIgnoreFunction(node: TSESTree.Node): boolean {
+      return (
+        !!options[OptionKeys.VariableDeclarationIgnoreFunction] &&
+        (node.type === AST_NODE_TYPES.FunctionExpression ||
+          node.type === AST_NODE_TYPES.ArrowFunctionExpression)
+      );
+    }
+
     return {
       ArrayPattern(node): void {
         if (
@@ -141,6 +151,10 @@ export default util.createRule<[Options], MessageIds>({
         }
       },
       ClassProperty(node): void {
+        if (node.value && isVariableDeclarationIgnoreFunction(node.value)) {
+          return;
+        }
+
         if (
           options[OptionKeys.MemberVariableDeclaration] &&
           !node.typeAnnotation
@@ -188,7 +202,8 @@ export default util.createRule<[Options], MessageIds>({
           (node.id.type === AST_NODE_TYPES.ArrayPattern &&
             !options[OptionKeys.ArrayDestructuring]) ||
           (node.id.type === AST_NODE_TYPES.ObjectPattern &&
-            !options[OptionKeys.ObjectDestructuring])
+            !options[OptionKeys.ObjectDestructuring]) ||
+          (node.init && isVariableDeclarationIgnoreFunction(node.init))
         ) {
           return;
         }

diff --git a/packages/eslint-plugin/tests/rules/typedef.test.ts b/packages/eslint-plugin/tests/rules/typedef.test.ts
@@ -302,6 +302,57 @@ ruleTester.run('typedef', rule, {
         },
       ],
     },
+    // variable declaration ignore function
+    {
+      code: `const foo = function(): void {};`,
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
+    {
+      code: `const foo = (): void => {};`,
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
+    {
+      code: `const foo: () => void = (): void => {};`,
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
+    {
+      code: `const foo: () => void = function (): void {};`,
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
+    {
+      code: `
+class Foo {
+  a = (): void => {};
+  b = function (): void {};
+}
+      `,
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
   ],
   invalid: [
     // Array destructuring
@@ -652,5 +703,74 @@ ruleTester.run('typedef', rule, {
         },
       ],
     },
+    {
+      code: `const foo = 'foo'`,
+      errors: [
+        {
+          messageId: 'expectedTypedefNamed',
+          data: { name: 'foo' },
+        },
+      ],
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: true,
+        },
+      ],
+    },
+    {
+      code: `const foo = function(): void {};`,
+      errors: [
+        {
+          messageId: 'expectedTypedefNamed',
+          data: { name: 'foo' },
+        },
+      ],
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: false,
+        },
+      ],
+    },
+    {
+      code: `const foo = (): void => {};`,
+      errors: [
+        {
+          messageId: 'expectedTypedefNamed',
+          data: { name: 'foo' },
+        },
+      ],
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: false,
+        },
+      ],
+    },
+    {
+      code: `
+class Foo {
+  a = (): void => {};
+  b = function (): void {};
+}
+      `,
+      errors: [
+        {
+          messageId: 'expectedTypedefNamed',
+          data: { name: 'a' },
+        },
+        {
+          messageId: 'expectedTypedefNamed',
+          data: { name: 'b' },
+        },
+      ],
+      options: [
+        {
+          variableDeclaration: true,
+          variableDeclarationIgnoreFunction: false,
+        },
+      ],
+    },
   ],
 });