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Merge pull request #721 from robertrossmann/prefer-single-export
New: `group-exports` rule
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,87 @@ | ||
| # group-exports | ||
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| Reports when named exports are not grouped together in a single `export` declaration or when multiple assignments to CommonJS `module.exports` or `exports` object are present in a single file. | ||
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| **Rationale:** An `export` declaration or `module.exports` assignment can appear anywhere in the code. By requiring a single export declaration all your exports will remain at one place, making it easier to see what exports a module provides. | ||
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| ## Rule Details | ||
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| This rule warns whenever a single file contains multiple named export declarations or multiple assignments to `module.exports` (or `exports`). | ||
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| ### Valid | ||
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| ```js | ||
| // A single named export declaration -> ok | ||
| export const valid = true | ||
| ``` | ||
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| ```js | ||
| const first = true | ||
| const second = true | ||
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| // A single named export declaration -> ok | ||
| export { | ||
| first, | ||
| second, | ||
| } | ||
| ``` | ||
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| ```js | ||
| // A single exports assignment -> ok | ||
| module.exports = { | ||
| first: true, | ||
| second: true | ||
| } | ||
| ``` | ||
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| ```js | ||
| const first = true | ||
| const second = true | ||
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| // A single exports assignment -> ok | ||
| module.exports = { | ||
| first, | ||
| second, | ||
| } | ||
| ``` | ||
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| ```js | ||
| function test() {} | ||
| test.property = true | ||
| test.another = true | ||
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| // A single exports assignment -> ok | ||
| module.exports = test | ||
| ``` | ||
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| ### Invalid | ||
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| ```js | ||
| // Multiple named export statements -> not ok! | ||
| export const first = true | ||
| export const second = true | ||
| ``` | ||
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| ```js | ||
| // Multiple exports assignments -> not ok! | ||
| exports.first = true | ||
| exports.second = true | ||
| ``` | ||
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| ```js | ||
| // Multiple exports assignments -> not ok! | ||
| module.exports = {} | ||
| module.exports.first = true | ||
| ``` | ||
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| ```js | ||
| // Multiple exports assignments -> not ok! | ||
| module.exports = () => {} | ||
| module.exports.first = true | ||
| module.exports.second = true | ||
| ``` | ||
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| ## When Not To Use It | ||
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| If you do not mind having your exports spread across the file, you can safely turn this rule off. |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,98 @@ | ||
| const meta = {} | ||
| /* eslint-disable max-len */ | ||
| const errors = { | ||
| ExportNamedDeclaration: 'Multiple named export declarations; consolidate all named exports into a single export declaration', | ||
| AssignmentExpression: 'Multiple CommonJS exports; consolidate all exports into a single assignment to `module.exports`', | ||
| } | ||
| /* eslint-enable max-len */ | ||
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| /** | ||
| * Returns an array with names of the properties in the accessor chain for MemberExpression nodes | ||
| * | ||
| * Example: | ||
| * | ||
| * `module.exports = {}` => ['module', 'exports'] | ||
| * `module.exports.property = true` => ['module', 'exports', 'property'] | ||
| * | ||
| * @param {Node} node AST Node (MemberExpression) | ||
| * @return {Array} Array with the property names in the chain | ||
| * @private | ||
| */ | ||
| function accessorChain(node) { | ||
| const chain = [] | ||
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| do { | ||
| chain.unshift(node.property.name) | ||
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| if (node.object.type === 'Identifier') { | ||
| chain.unshift(node.object.name) | ||
| break | ||
| } | ||
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| node = node.object | ||
| } while (node.type === 'MemberExpression') | ||
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| return chain | ||
| } | ||
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| function create(context) { | ||
| const nodes = { | ||
| modules: new Set(), | ||
| commonjs: new Set(), | ||
| } | ||
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| return { | ||
| ExportNamedDeclaration(node) { | ||
| nodes.modules.add(node) | ||
| }, | ||
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| AssignmentExpression(node) { | ||
| if (node.left.type !== 'MemberExpression') { | ||
| return | ||
| } | ||
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| const chain = accessorChain(node.left) | ||
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| // Assignments to module.exports | ||
| // Deeper assignments are ignored since they just modify what's already being exported | ||
| // (ie. module.exports.exported.prop = true is ignored) | ||
| if (chain[0] === 'module' && chain[1] === 'exports' && chain.length <= 3) { | ||
| nodes.commonjs.add(node) | ||
| return | ||
| } | ||
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| // Assignments to exports (exports.* = *) | ||
| if (chain[0] === 'exports' && chain.length === 2) { | ||
| nodes.commonjs.add(node) | ||
| return | ||
| } | ||
| }, | ||
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| 'Program:exit': function onExit() { | ||
| // Report multiple `export` declarations (ES2015 modules) | ||
| if (nodes.modules.size > 1) { | ||
| nodes.modules.forEach(node => { | ||
| context.report({ | ||
| node, | ||
| message: errors[node.type], | ||
| }) | ||
| }) | ||
| } | ||
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| // Report multiple `module.exports` assignments (CommonJS) | ||
| if (nodes.commonjs.size > 1) { | ||
| nodes.commonjs.forEach(node => { | ||
| context.report({ | ||
| node, | ||
| message: errors[node.type], | ||
| }) | ||
| }) | ||
| } | ||
| }, | ||
| } | ||
| } | ||
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| export default { | ||
| meta, | ||
| create, | ||
| } |
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