perf: Use === or Set.has instead of array.indexOf for keyword checks

packages/babel-parser/src/parser/base.js

@@ -1,7 +1,7 @@
 // @flow
 
 import type { Options } from "../options";
-import { reservedWords } from "../util/identifier";
+import { isES2015ReservedWord } from "../util/identifier";
 
 import type State from "../tokenizer/state";
 import type { PluginsMap } from "./index";
@@ -21,7 +21,7 @@ export default class BaseParser {
     if (word === "await") {
       return this.inModule;
     } else {
-      return reservedWords[6](word);
+      return isES2015ReservedWord(word);
     }
   }
 

packages/babel-parser/src/parser/expression.js

@@ -21,7 +21,10 @@
 import { types as tt, type TokenType } from "../tokenizer/types";
 import * as N from "../types";
 import LValParser from "./lval";
-import { reservedWords } from "../util/identifier";
+import {
+  isStrictReservedWord,
+  isStrictBindReservedWord,
+} from "../util/identifier";
 import type { Pos, Position } from "../util/location";
 import * as charCodes from "charcodes";
 
@@ -1997,8 +2000,8 @@ export default class ExpressionParser extends LValParser {
   ): void {
     if (
       this.state.strict &&
-      (reservedWords.strict(word) ||
+      (isStrictReservedWord(word) ||
-        (isBinding && reservedWords.strictBind(word)))
+        (isBinding && isStrictBindReservedWord(word)))
     ) {
       this.raise(startLoc, word + " is a reserved word in strict mode");
     }

packages/babel-parser/src/util/identifier.js

@@ -4,28 +4,72 @@
 
 import * as charCodes from "charcodes";
 
-function makePredicate(words: string): (str: string) => boolean {
+export const isES2015ReservedWord = (word: string): boolean => {
-  const wordsArr = words.split(" ");
+  return word === "enum" || word === "await";
-  return function(str) {
-    return wordsArr.indexOf(str) >= 0;
 };
+
+const reservedWordsStrict = new Set([
+  "implements",
+  "interface",
+  "let",
+  "package",
+  "private",
+  "protected",
+  "public",
+  "static",
+  "yield",
+]);
+export function isStrictReservedWord(word: string): boolean {
+  return reservedWordsStrict.has(word);
 }
 
-// Reserved word lists for various dialects of the language
+export function isStrictBindReservedWord(word: string): boolean {
+  return word === "eval" || word === "arguments";
+}
 
-export const reservedWords = {
+const keywords = new Set([
-  "6": makePredicate("enum await"),
+  "break",
-  strict: makePredicate(
+  "case",
-    "implements interface let package private protected public static yield",
+  "catch",
-  ),
+  "continue",
-  strictBind: makePredicate("eval arguments"),
+  "debugger",
-};
+  "default",
+  "do",
+  "else",
+  "finally",
+  "for",
+  "function",
+  "if",
+  "return",
+  "switch",
+  "throw",
+  "try",
+  "var",
+  "while",
+  "with",
+  "null",
+  "true",
+  "false",
+  "instanceof",
+  "typeof",
+  "void",
+  "delete",
+  "new",
+  "in",
+  "this",
+  "let",
+  "const",
+  "class",
+  "extends",
+  "export",
+  "import",
+  "yield",
+  "super",
+]);
 
-// And the keywords
+export function isKeyword(word: string): boolean {
-
+  return keywords.has(word);
-export const isKeyword = makePredicate(
+}
-  "break case catch continue debugger default do else finally for function if return switch throw try var while with null true false instanceof typeof void delete new in this let const class extends export import yield super",
-);
 
 // ## Character categories
 

packages/babel-parser/test/unit/util/identifier.js

@@ -0,0 +1,18 @@
+import { isKeyword } from "../../../src/util/identifier";
+
+describe("identifier", () => {
+  describe("isKeyword", () => {
+    it("break is a keyword", () => {
+      expect(isKeyword("break")).toBe(true);
+    });
+    it("let is a keyword", () => {
+      expect(isKeyword("let")).toBe(true);
+    });
+    it("super is a keyword", () => {
+      expect(isKeyword("super")).toBe(true);
+    });
+    it("abc is not a keyword", () => {
+      expect(isKeyword("abc")).toBe(false);
+    });
+  });
+});