[Refactor] no-duplicates, no-unused-modules: use flatMap instead of map + filter

Author: ljharb

src/rules/no-default-export.js

@@ -27,14 +27,16 @@ module.exports = {
       },
 
       ExportNamedDeclaration(node) {
-        node.specifiers.filter((specifier) => (specifier.exported.name || specifier.exported.value) === 'default').forEach((specifier) => {
-          const { loc } = context.getSourceCode().getFirstTokens(node)[1] || {};
-          if (specifier.type === 'ExportDefaultSpecifier') {
-            context.report({ node, message: preferNamed, loc });
-          } else if (specifier.type === 'ExportSpecifier') {
-            context.report({ node, message: noAliasDefault(specifier), loc  });
-          }
-        });
+        node.specifiers
+          .filter((specifier) => (specifier.exported.name || specifier.exported.value) === 'default')
+          .forEach((specifier) => {
+            const { loc } = context.getSourceCode().getFirstTokens(node)[1] || {};
+            if (specifier.type === 'ExportDefaultSpecifier') {
+              context.report({ node, message: preferNamed, loc });
+            } else if (specifier.type === 'ExportSpecifier') {
+              context.report({ node, message: noAliasDefault(specifier), loc  });
+            }
+          });
       },
     };
   },

src/rules/no-duplicates.js

@@ -1,6 +1,8 @@
 import resolve from 'eslint-module-utils/resolve';
-import docsUrl from '../docsUrl';
 import semver from 'semver';
+import flatMap from 'array.prototype.flatmap';
+
+import docsUrl from '../docsUrl';
 
 let typescriptPkg;
 try {
@@ -51,7 +53,7 @@ function getFix(first, rest, sourceCode, context) {
   }
 
   const defaultImportNames = new Set(
-    [first, ...rest].map(getDefaultImportName).filter(Boolean),
+    flatMap([].concat(first, rest || []), (x) => getDefaultImportName(x) || []),
   );
 
   // Bail if there are multiple different default import names – it's up to the
@@ -62,10 +64,7 @@ function getFix(first, rest, sourceCode, context) {
 
   // Leave it to the user to handle comments. Also skip `import * as ns from
   // './foo'` imports, since they cannot be merged into another import.
-  const restWithoutComments = rest.filter((node) => !(
-    hasProblematicComments(node, sourceCode)
-    || hasNamespace(node)
-  ));
+  const restWithoutComments = rest.filter((node) => !hasProblematicComments(node, sourceCode) && !hasNamespace(node));
 
   const specifiers = restWithoutComments
     .map((node) => {

src/rules/no-restricted-paths.js

@@ -77,9 +77,11 @@ module.exports = {
     const restrictedPaths = options.zones || [];
     const basePath = options.basePath || process.cwd();
     const currentFilename = context.getPhysicalFilename ? context.getPhysicalFilename() : context.getFilename();
-    const matchingZones = restrictedPaths.filter((zone) => [].concat(zone.target)
-      .map((target) => path.resolve(basePath, target))
-      .some((targetPath) => isMatchingTargetPath(currentFilename, targetPath)));
+    const matchingZones = restrictedPaths.filter(
+      (zone) => [].concat(zone.target)
+        .map((target) => path.resolve(basePath, target))
+        .some((targetPath) => isMatchingTargetPath(currentFilename, targetPath)),
+    );
 
     function isMatchingTargetPath(filename, targetPath) {
       if (isGlob(targetPath)) {
@@ -231,8 +233,7 @@ module.exports = {
         reportInvalidExceptions(validatorsWithInvalidExceptions, node);
 
         const applicableValidatorsForImportPathExcludingExceptions = applicableValidatorsForImportPath
-          .filter((validator) => validator.hasValidExceptions)
-          .filter((validator) => !validator.isPathException(absoluteImportPath));
+          .filter((validator) => validator.hasValidExceptions && !validator.isPathException(absoluteImportPath));
         reportImportsInRestrictedZone(applicableValidatorsForImportPathExcludingExceptions, node, importPath, zone.message);
       });
     }

src/rules/no-unused-modules.js

@@ -177,7 +177,7 @@ const resolveFiles = (src, ignoreExports, context) => {
   // prepare list of source files, don't consider files from node_modules
 
   return new Set(
-    srcFileList.filter(({ filename }) => !isNodeModule(filename)).map(({ filename }) => filename),
+    flatMap(srcFileList, ({ filename }) => isNodeModule(filename) ? [] : filename),
   );
 };
 
@@ -359,9 +359,7 @@ const fileIsInPkg = (file) => {
   };
 
   const checkPkgFieldObject = (pkgField) => {
-    const pkgFieldFiles = values(pkgField)
-      .filter((value) => typeof value !== 'boolean')
-      .map((value) => join(basePath, value));
+    const pkgFieldFiles = flatMap(values(pkgField), (value) => typeof value === 'boolean' ? [] : join(basePath, value));
 
     if (includes(pkgFieldFiles, file)) {
       return true;

tests/src/package.js

@@ -27,8 +27,7 @@ describe('package', function () {
         expect(err).not.to.exist;
 
         files.filter(isJSFile).forEach(function (f) {
-          expect(module.rules).to.have
-            .property(path.basename(f, '.js'));
+          expect(module.rules).to.have.property(path.basename(f, '.js'));
         });
 
         done();

tests/src/rules/order.js

@@ -2736,7 +2736,7 @@ ruleTester.run('order', rule, {
         }],
       }),
     ],
-  ].filter((t) => !!t),
+  ].filter(Boolean),
 });
 
 context('TypeScript', function () {