Add no-anonymous-default-export rule

CHANGELOG.md

@@ -4,6 +4,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This change log adheres to standards from [Keep a CHANGELOG](http://keepachangelog.com).
 
 ## [Unreleased]
+### Added
+- [`no-anonymous-default-export`] rule: report anonymous default exports.
+
 ### Changed
 - [`no-extraneous-dependencies`]: use `read-pkg-up` to simplify finding + loading `package.json` ([#680], thanks [@wtgtybhertgeghgtwtg])
 

README.md

@@ -76,6 +76,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 * Limit the maximum number of dependencies a module can have ([`max-dependencies`])
 * Forbid unassigned imports ([`no-unassigned-import`])
 * Forbid named default exports ([`no-named-default`])
+* Forbid anonymous values as default exports ([`no-anonymous-default-export`])
 
 [`first`]: ./docs/rules/first.md
 [`no-duplicates`]: ./docs/rules/no-duplicates.md
@@ -87,6 +88,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 [`max-dependencies`]: ./docs/rules/max-dependencies.md
 [`no-unassigned-import`]: ./docs/rules/no-unassigned-import.md
 [`no-named-default`]: ./docs/rules/no-named-default.md
+[`no-anonymous-default-export`]: ./docs/rules/no-anonymous-default-export.md
 
 ## Installation
 

docs/rules/no-anonymous-default-export.md

@@ -0,0 +1,45 @@
+# no-anonymous-default-export
+
+Reports if a module's default export is unnamed. This includes several types of unnamed data types; literals, object expressions, anonymous functions, arrow functions, and anonymous class declarations.
+
+Ensuring that default exports are named helps improve the grepability of the codebase by encouraging the re-use of the same identifier for the module's default export at its declaration site and at its import sites.
+
+By default, all types of anonymous default exports are forbidden, but each type can be selectively allowed using options.
+
+## Rule Details
+
+### Fail
+```js
+export default 123
+
+export default {}
+
+export default function () {}
+
+export default () => {}
+
+export default class {}
+```
+
+### Pass
+```js
+const foo = 123
+export default foo
+
+export default function foo() {}
+
+/*eslint no-anonymous-default-export: [2, "allow-literal"]*/
+export default 123
+
+/*eslint no-anonymous-default-export: [2, "object-expression"]*/
+export default {}
+
+/*eslint no-anonymous-default-export: [2, "allow-anonymous-function-declaration"]*/
+export default function () {}
+
+/*eslint no-anonymous-default-export: [2, "allow-arrow-function-expression"]*/
+export default () => {}
+
+/*eslint no-anonymous-default-export: [2, "allow-anonymous-class-declaration"]*/
+export default class {}
+```

src/index.js

@@ -13,6 +13,7 @@ export const rules = {
   'no-named-default': require('./rules/no-named-default'),
   'no-named-as-default': require('./rules/no-named-as-default'),
   'no-named-as-default-member': require('./rules/no-named-as-default-member'),
+  'no-anonymous-default-export': require('./rules/no-anonymous-default-export'),
 
   'no-commonjs': require('./rules/no-commonjs'),
   'no-amd': require('./rules/no-amd'),

src/rules/no-anonymous-default-export.js

@@ -0,0 +1,61 @@
+/**
+ * @fileoverview Rule to disallow anonymous default exports.
+ * @author Duncan Beevers
+ */
+
+module.exports = {
+  meta: {},
+
+  create: function (context) {
+
+    const forbid = (option) => !~context.options.indexOf('allow-' + option)
+
+    return {
+      'ExportDefaultDeclaration': (node) => {
+        const type = node.declaration.type
+        const noID = !node.declaration.id
+
+        if (type === 'Literal' && forbid('literal')) {
+          context.report({
+            node: node,
+            message: 'Unexpected default export of literal',
+          })
+          return
+        }
+
+        if (type === 'ObjectExpression' && forbid('object-expression')) {
+          context.report({
+            node: node,
+            message: 'Unexpected default export of object expression',
+          })
+          return
+        }
+
+        if (type === 'FunctionDeclaration' && noID && forbid('anonymous-function-declaration')) {
+          context.report({
+            node: node,
+            message: 'Unexpected default export of anonymous function',
+          })
+          return
+        }
+
+        if (type === 'ArrowFunctionExpression' && forbid('arrow-function-expression')) {
+          context.report({
+            node: node,
+            message: 'Unexpected default export of arrow function',
+          })
+          return
+        }
+
+        if (type === 'ClassDeclaration' && noID && forbid('anonymous-class-declaration')) {
+          context.report({
+            node: node,
+            message: 'Unexpected default export of anonymous class',
+          })
+          return
+        }
+      },
+    }
+
+  },
+}

tests/src/rules/no-anonymous-default-export.js

@@ -0,0 +1,30 @@
+import { test, SYNTAX_CASES } from '../utils'
+
+import { RuleTester } from 'eslint'
+
+var ruleTester = new RuleTester()
+var rule = require('rules/no-anonymous-default-export')
+
+ruleTester.run('no-anonymous-default-export', rule, {
+    valid: [
+      test({ code: 'const foo = 123\nexport default foo' }),
+      test({ code: 'export default function foo() {}'}),
+      test({ code: 'export default class MyClass {}'}),
+
+      test({ code: 'export default 123', options: ['allow-literal'] }),
+      test({ code: 'export default {}', options: ['allow-object-expression'] }),
+      test({ code: 'export default class {}', options: ['allow-anonymous-class-declaration'] }),
+      test({ code: 'export default function() {}', options: ['allow-anonymous-function-declaration'] }),
+      test({ code: 'export default () => {}', options: ['allow-arrow-function-expression'] }),
+
+      ...SYNTAX_CASES,
+    ],
+
+    invalid: [
+      test({ code: 'export default 123', errors: [{ message: 'Unexpected default export of literal' }] }),
+      test({ code: 'export default {}', errors: [{ message: 'Unexpected default export of object expression' }] }),
+      test({ code: 'export default class {}', errors: [{ message: 'Unexpected default export of anonymous class' }] }),
+      test({ code: 'export default function() {}', errors: [{ message: 'Unexpected default export of anonymous function' }] }),
+      test({ code: 'export default () => {}', errors: [{ message: 'Unexpected default export of arrow function' }] }),
+    ],
+})