exports-last

CHANGELOG.md

@@ -6,8 +6,8 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 ## [Unreleased]
 ### Added
 - [`no-anonymous-default-export`] rule: report anonymous default exports ([#712], thanks [@duncanbeevers]).
-- Add new value to [`order`]'s `newlines-between` option to allow newlines inside import groups ([#627], [#628], thanks [@giodamelio])
-- Add `count` option to the [`newline-after-import`] rule to allow configuration of number of newlines expected ([#742], thanks [@ntdb])
+- Add new value to `order`'s `newlines-between` option to allow newlines inside import groups ([#627], [#628], thanks [@giodamelio])
+- [`exports-last`] lints that export statements are at the end of the file ([#620] + [#632])
 
 ### Changed
 - [`no-extraneous-dependencies`]: use `read-pkg-up` to simplify finding + loading `package.json` ([#680], thanks [@wtgtybhertgeghgtwtg])

README.md

@@ -67,6 +67,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 **Style guide:**
 
 * Ensure all imports appear before other statements ([`first`])
+* Ensure all exports appear after other statements ([`exports-last`])
 * Report repeated import of the same module in multiple places ([`no-duplicates`])
 * Report namespace imports ([`no-namespace`])
 * Ensure consistent use of file extension within the import path ([`extensions`])
@@ -79,6 +80,7 @@ This plugin intends to support linting of ES2015+ (ES6+) import/export syntax, a
 * Forbid anonymous values as default exports ([`no-anonymous-default-export`])
 
 [`first`]: ./docs/rules/first.md
+[`exports-last`]: ./docs/rules/exports-last.md
 [`no-duplicates`]: ./docs/rules/no-duplicates.md
 [`no-namespace`]: ./docs/rules/no-namespace.md
 [`extensions`]: ./docs/rules/extensions.md

docs/rules/exports-last.md

@@ -0,0 +1,50 @@
+# exports-last
+
+This rule enforces that all exports are declared at the bottom of the file. This rule will report any export declarations that comes before any non-export statements.
+
+
+## This will be reported
+
+```JS
+
+const bool = true
+
+export default bool
+
+const str = 'foo'
+
+```
+
+```JS
+
+export const bool = true
+
+const str = 'foo'
+
+```
+
+## This will not be reported
+
+```JS
+const arr = ['bar']
+
+export const bool = true
+
+export default bool
+
+export function func() {
+  console.log('Hello World 🌍')
+}
+
+export const str = 'foo'
+```
+
+## When Not To Use It
+
+If you don't mind exports being sprinkled throughout a file, you may not want to enable this rule.
+
+#### ES6 exports only
+
+The exports-last rule is currently only working on ES6 exports. You may not want to enable this rule if you're using CommonJS exports.
+
+If you need CommonJS support feel free to open an issue or create a PR.

src/index.js

@@ -31,6 +31,9 @@ export const rules = {
   'unambiguous': require('./rules/unambiguous'),
   'no-unassigned-import': require('./rules/no-unassigned-import'),
 
+  // export
+  'exports-last': require('./rules/exports-last'),
+
   // metadata-based
   'no-deprecated': require('./rules/no-deprecated'),
 

src/rules/exports-last.js

@@ -0,0 +1,31 @@
+function isNonExportStatement({ type }) {
+  return type !== 'ExportDefaultDeclaration' &&
+    type !== 'ExportNamedDeclaration' &&
+    type !== 'ExportAllDeclaration'
+}
+
+module.exports = {
+  create: function (context) {
+    return {
+      Program: function ({ body }) {
+        const lastNonExportStatementIndex = body.reduce(function findLastIndex(acc, item, index) {
+          if (isNonExportStatement(item)) {
+            return index
+          }
+          return acc
+        }, -1)
+
+        if (lastNonExportStatementIndex !== -1) {
+          body.slice(0, lastNonExportStatementIndex).forEach(function checkNonExport(node) {
+            if (!isNonExportStatement(node)) {
+              context.report({
+                node,
+                message: 'Export statements should appear at the end of the file',
+              })
+            }
+          })
+        }
+      },
+    }
+  },
+}

tests/src/rules/exports-last.js

@@ -0,0 +1,124 @@
+import { test } from '../utils'
+
+import { RuleTester } from 'eslint'
+import rule from 'rules/exports-last'
+
+const ruleTester = new RuleTester()
+
+const error = type => ({
+  ruleId: 'exports-last',
+  message: 'Export statements should appear at the end of the file',
+  type
+});
+
+ruleTester.run('exports-last', rule, {
+  valid: [
+    // Empty file
+    test({
+      code: '// comment',
+    }),
+    test({
+      // No exports
+      code: `
+        const foo = 'bar'
+        const bar = 'baz'
+      `,
+    }),
+    test({
+      code: `
+        const foo = 'bar'
+        export {foo}
+      `,
+    }),
+    test({
+      code: `
+        const foo = 'bar'
+        export default foo
+      `,
+    }),
+    // Only exports
+    test({
+      code: `
+        export default foo
+        export const bar = true
+      `,
+    }),
+    test({
+      code: `
+        const foo = 'bar'
+        export default foo
+        export const bar = true
+      `,
+    }),
+    // Multiline export
+    test({
+      code: `
+        const foo = 'bar'
+        export default function foo () {
+          const very = 'multiline'
+        }
+        export const bar = true
+      `,
+    }),
+    // Many exports
+    test({
+      code: `
+        const foo = 'bar'
+        export default foo
+        export const so = 'many'
+        export const exports = ':)'
+        export const i = 'cant'
+        export const even = 'count'
+        export const how = 'many'
+      `,
+    }),
+    // Export all
+    test({
+      code: `
+        export * from './foo'
+      `,
+    }),
+  ],
+  invalid: [
+    // Default export before variable declaration
+    test({
+      code: `
+        export default 'bar'
+        const bar = true
+      `,
+      errors: [error('ExportDefaultDeclaration')],
+    }),
+    // Named export before variable declaration
+    test({
+      code: `
+        export const foo = 'bar'
+        const bar = true
+      `,
+      errors: [error('ExportNamedDeclaration')],
+    }),
+    // Export all before variable declaration
+    test({
+      code: `
+        export * from './foo'
+        const bar = true
+      `,
+      errors: [error('ExportAllDeclaration')],
+    }),
+    // Many exports arround variable declaration
+    test({
+      code: `
+        export default 'such foo many bar'
+        export const so = 'many'
+        const foo = 'bar'
+        export const exports = ':)'
+        export const i = 'cant'
+        export const even = 'count'
+        export const how = 'many'
+      `,
+      errors: [
+        error('ExportDefaultDeclaration'),
+        error('ExportNamedDeclaration'),
+      ],
+    }),
+  ],
+})