typescript-eslint · bradzacher · May 10, 2019 · Feb 20, 2019 · Feb 20, 2019 · Feb 20, 2019
diff --git a/packages/eslint-plugin/README.md b/packages/eslint-plugin/README.md
@@ -162,6 +162,7 @@ Then you should add `airbnb` (or `airbnb-base`) to your `extends` section of `.e
 | [`@typescript-eslint/semi`](./docs/rules/semi.md)                                                         | Require or disallow semicolons instead of ASI                                                                                                       |                    | :wrench: |                   |
 | [`@typescript-eslint/type-annotation-spacing`](./docs/rules/type-annotation-spacing.md)                   | Require consistent spacing around type annotations (`typedef-whitespace` from TSLint)                                                               | :heavy_check_mark: | :wrench: |                   |
 | [`@typescript-eslint/unbound-method`](./docs/rules/unbound-method.md)                                     | Enforces unbound methods are called with their expected scope. (`no-unbound-method` from TSLint)                                                    | :heavy_check_mark: |          | :thought_balloon: |
+| [`@typescript-eslint/prefer-regexp-exec`](./docs/rules/prefer-regexp-exec.md)                             | Enforce to use `RegExp#exec` over `String#match`                                                                                                    |                    |          | :thought_balloon: |
 | [`@typescript-eslint/unified-signatures`](./docs/rules/unified-signatures.md)                             | Warns for any two overloads that could be unified into one. (`unified-signatures` from TSLint)                                                      |                    |          |                   |
 
 <!-- end rule list -->
diff --git a/packages/eslint-plugin/docs/rules/prefer-regexp-exec.md b/packages/eslint-plugin/docs/rules/prefer-regexp-exec.md
@@ -0,0 +1,53 @@
+# Enforce to use `RegExp#exec` over `String#match` (prefer-regexp-exec)
+
+`RegExp#exec` is faster than `String#match` and both work the same when not using the `/g` flag.
+
+## Rule Details
+
+This rule is aimed at enforcing the more performant way of applying regular expressions on strings.
+
+From [`String#match` on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/match):
+
+> If the regular expression does not include the g flag, returns the same result as RegExp.exec().
+
+From [Stack Overflow](https://stackoverflow.com/questions/9214754/what-is-the-difference-between-regexp-s-exec-function-and-string-s-match-fun)
+
+> `RegExp.prototype.exec` is a lot faster than `String.prototype.match`, but that’s because they are not exactly the same thing, they are different.
+
+Examples of **incorrect** code for this rule:
+
+```ts
+'something'.match(/thing/);
+
+'some things are just things'.match(/thing/);
+
+const text = 'something';
+const search = /thing/;
+text.match(search);
+```
+
+Examples of **correct** code for this rule:
+
+```ts
+/thing/.exec('something');
+
+'some things are just things'.match(/thing/g);
+
+const text = 'something';
+const search = /thing/;
+search.exec(text);
+```
+
+## Options
+
+There are no options.
+
+```json
+{
+  "@typescript-eslint/prefer-regexp-exec": "error"
+}
+```
+
+## When Not To Use It
+
+If you prefer consistent use of `String#match` for both, with `g` flag and without it, you can turn this rule off.
diff --git a/packages/eslint-plugin/src/rules/prefer-regexp-exec.ts b/packages/eslint-plugin/src/rules/prefer-regexp-exec.ts
@@ -0,0 +1,66 @@
+import { TSESTree } from '@typescript-eslint/typescript-estree';
+import { createRule, getParserServices, getTypeName } from '../util';
+import { getStaticValue } from 'eslint-utils';
+
+export default createRule({
+  name: 'prefer-regexp-exec',
+  defaultOptions: [],
+
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description:
+        'Prefer RegExp#exec() over String#match() if no global flag is provided.',
+      category: 'Best Practices',
+      recommended: false,
+    },
+    messages: {
+      regExpExecOverStringMatch: 'Use the `RegExp#exec()` method instead.',
+    },
+    schema: [],
+  },
+
+  create(context) {
+    const globalScope = context.getScope();
+    const service = getParserServices(context);
+    const typeChecker = service.program.getTypeChecker();
+
+    /**
+     * Check if a given node is a string.
+     * @param node The node to check.
+     */
+    function isStringType(node: TSESTree.Node): boolean {
+      const objectType = typeChecker.getTypeAtLocation(
+        service.esTreeNodeToTSNodeMap.get(node),
+      );
+      return getTypeName(typeChecker, objectType) === 'string';
+    }
+
+    return {
+      "CallExpression[arguments.length=1] > MemberExpression.callee[property.name='match'][computed=false]"(
+        node: TSESTree.MemberExpression,
+      ) {
+        const callNode = node.parent as TSESTree.CallExpression;
+        const arg = callNode.arguments[0];
+        const evaluated = getStaticValue(arg, globalScope);
+
+        // Don't report regular expressions with global flag.
+        if (
+          evaluated &&
+          evaluated.value instanceof RegExp &&
+          evaluated.value.flags.includes('g')
+        ) {
+          return;
+        }
+
+        if (isStringType(node.object)) {
+          context.report({
+            node: callNode,
+            messageId: 'regExpExecOverStringMatch',
+          });
+          return;
+        }
+      },
+    };
+  },
+});
diff --git a/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts b/packages/eslint-plugin/src/rules/prefer-string-starts-ends-with.ts
@@ -5,8 +5,7 @@ import {
   getStaticValue,
 } from 'eslint-utils';
 import { RegExpParser, AST as RegExpAST } from 'regexpp';
-import ts from 'typescript';
-import { createRule, getParserServices } from '../util';
+import { createRule, getParserServices, getTypeName } from '../util';
 
 const EQ_OPERATORS = /^[=!]=/;
 const regexpp = new RegExpParser();
@@ -35,65 +34,17 @@ export default createRule({
     const globalScope = context.getScope();
     const sourceCode = context.getSourceCode();
     const service = getParserServices(context);
-    const types = service.program.getTypeChecker();
-
-    /**
-     * Get the type name of a given type.
-     * @param type The type to get.
-     */
-    function getTypeName(type: ts.Type): string {
-      // It handles `string` and string literal types as string.
-      if ((type.flags & ts.TypeFlags.StringLike) !== 0) {
-        return 'string';
-      }
-
-      // If the type is a type parameter which extends primitive string types,
-      // but it was not recognized as a string like. So check the constraint
-      // type of the type parameter.
-      if ((type.flags & ts.TypeFlags.TypeParameter) !== 0) {
-        // `type.getConstraint()` method doesn't return the constraint type of
-        // the type parameter for some reason. So this gets the constraint type
-        // via AST.
-        const node = type.symbol.declarations[0] as ts.TypeParameterDeclaration;
-        if (node.constraint != null) {
-          return getTypeName(types.getTypeFromTypeNode(node.constraint));
-        }
-      }
-
-      // If the type is a union and all types in the union are string like,
-      // return `string`. For example:
-      // - `"a" | "b"` is string.
-      // - `string | string[]` is not string.
-      if (
-        type.isUnion() &&
-        type.types.map(getTypeName).every(t => t === 'string')
-      ) {
-        return 'string';
-      }
-
-      // If the type is an intersection and a type in the intersection is string
-      // like, return `string`. For example: `string & {__htmlEscaped: void}`
-      if (
-        type.isIntersection() &&
-        type.types.map(getTypeName).some(t => t === 'string')
-      ) {
-        return 'string';
-      }
-
-      return types.typeToString(type);
-    }
+    const typeChecker = service.program.getTypeChecker();
 
     /**
      * Check if a given node is a string.
      * @param node The node to check.
      */
     function isStringType(node: TSESTree.Node): boolean {
-      const objectType = types.getTypeAtLocation(
+      const objectType = typeChecker.getTypeAtLocation(
         service.esTreeNodeToTSNodeMap.get(node),
       );
-      const typeName = getTypeName(objectType);
-
-      return typeName === 'string';
+      return getTypeName(typeChecker, objectType) === 'string';
     }
 
     /**

diff --git a/packages/eslint-plugin/src/util/types.ts b/packages/eslint-plugin/src/util/types.ts
@@ -41,6 +41,63 @@ export function containsTypeByName(
   );
 }
 
+/**
+ * Get the type name of a given type.
+ * @param typeChecker The context sensitive TypeScript TypeChecker.
+ * @param type The type to get the name of.
+ */
+export function getTypeName(
+  typeChecker: ts.TypeChecker,
+  type: ts.Type,
+): string {
+  // It handles `string` and string literal types as string.
+  if ((type.flags & ts.TypeFlags.StringLike) !== 0) {
+    return 'string';
+  }
+
+  // If the type is a type parameter which extends primitive string types,
+  // but it was not recognized as a string like. So check the constraint
+  // type of the type parameter.
+  if ((type.flags & ts.TypeFlags.TypeParameter) !== 0) {
+    // `type.getConstraint()` method doesn't return the constraint type of
+    // the type parameter for some reason. So this gets the constraint type
+    // via AST.
+    const node = type.symbol.declarations[0] as ts.TypeParameterDeclaration;
+    if (node.constraint != null) {
+      return getTypeName(
+        typeChecker,
+        typeChecker.getTypeFromTypeNode(node.constraint),
+      );
+    }
+  }
+
+  // If the type is a union and all types in the union are string like,
+  // return `string`. For example:
+  // - `"a" | "b"` is string.
+  // - `string | string[]` is not string.
+  if (
+    type.isUnion() &&
+    type.types
+      .map(value => getTypeName(typeChecker, value))
+      .every(t => t === 'string')
+  ) {
+    return 'string';
+  }
+
+  // If the type is an intersection and a type in the intersection is string
+  // like, return `string`. For example: `string & {__htmlEscaped: void}`
+  if (
+    type.isIntersection() &&
+    type.types
+      .map(value => getTypeName(typeChecker, value))
+      .some(t => t === 'string')
+  ) {
+    return 'string';
+  }
+
+  return typeChecker.typeToString(type);
+}
+
 /**
  * Resolves the given node's type. Will resolve to the type's generic constraint, if it has one.
  */