no-duplicate-imports.js
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/**
* @fileoverview Restrict usage of duplicate imports.
* @author Simen Bekkhus
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/**
* Returns the name of the module imported or re-exported.
* @param {ASTNode} node A node to get.
* @returns {string} the name of the module, or empty string if no name.
*/
function getValue(node) {
if (node && node.source && node.source.value) {
return node.source.value.trim();
}
return "";
}
/**
* Checks if the name of the import or export exists in the given array, and reports if so.
* @param {RuleContext} context The ESLint rule context object.
* @param {ASTNode} node A node to get.
* @param {string} value The name of the imported or exported module.
* @param {string[]} array The array containing other imports or exports in the file.
* @param {string} messageId A messageId to be reported after the name of the module
*
* @returns {void} No return value
*/
function checkAndReport(context, node, value, array, messageId) {
if (array.indexOf(value) !== -1) {
context.report({
node,
messageId,
data: {
module: value
}
});
}
}
/**
* @callback nodeCallback
* @param {ASTNode} node A node to handle.
*/
/**
* Returns a function handling the imports of a given file
* @param {RuleContext} context The ESLint rule context object.
* @param {boolean} includeExports Whether or not to check for exports in addition to imports.
* @param {string[]} importsInFile The array containing other imports in the file.
* @param {string[]} exportsInFile The array containing other exports in the file.
*
* @returns {nodeCallback} A function passed to ESLint to handle the statement.
*/
function handleImports(context, includeExports, importsInFile, exportsInFile) {
return function(node) {
const value = getValue(node);
if (value) {
checkAndReport(context, node, value, importsInFile, "import");
if (includeExports) {
checkAndReport(context, node, value, exportsInFile, "importAs");
}
importsInFile.push(value);
}
};
}
/**
* Returns a function handling the exports of a given file
* @param {RuleContext} context The ESLint rule context object.
* @param {string[]} importsInFile The array containing other imports in the file.
* @param {string[]} exportsInFile The array containing other exports in the file.
*
* @returns {nodeCallback} A function passed to ESLint to handle the statement.
*/
function handleExports(context, importsInFile, exportsInFile) {
return function(node) {
const value = getValue(node);
if (value) {
checkAndReport(context, node, value, exportsInFile, "export");
checkAndReport(context, node, value, importsInFile, "exportAs");
exportsInFile.push(value);
}
};
}
module.exports = {
meta: {
type: "problem",
docs: {
description: "disallow duplicate module imports",
category: "ECMAScript 6",
recommended: false,
url: "https://eslint.org/docs/rules/no-duplicate-imports"
},
schema: [{
type: "object",
properties: {
includeExports: {
type: "boolean",
default: false
}
},
additionalProperties: false
}],
messages: {
import: "'{{module}}' import is duplicated.",
importAs: "'{{module}}' import is duplicated as export.",
export: "'{{module}}' export is duplicated.",
exportAs: "'{{module}}' export is duplicated as import."
}
},
create(context) {
const includeExports = (context.options[0] || {}).includeExports,
importsInFile = [],
exportsInFile = [];
const handlers = {
ImportDeclaration: handleImports(context, includeExports, importsInFile, exportsInFile)
};
if (includeExports) {
handlers.ExportNamedDeclaration = handleExports(context, importsInFile, exportsInFile);
handlers.ExportAllDeclaration = handleExports(context, importsInFile, exportsInFile);
}
return handlers;
}
};