[reserved-words] add type definitions for the reserved-words package (#33741)

* add reserved-words type definitions

* Review feedback: remove namespace, esModuleInterop and add KEYWORDS

types/reserved-words/index.d.ts

@@ -0,0 +1,40 @@
+// Type definitions for reserved-words 0.1
+// Project: https://github.com/zxqfox/reserved-words#readme
+// Definitions by: Spencer Miskoviak <https://github.com/skovy>
+// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+// TypeScript Version: 3.0
+
+export type Dialect =
+    | "es3"
+    | 3
+    | "es5"
+    | 5
+    | "es2015"
+    | 6
+    | "es7"
+    | 7
+    | "es6"
+    | "next";
+
+export interface Keywords {
+    [index: string]: {
+        [index: string]: true;
+    };
+}
+
+export const KEYWORDS: Keywords;
+
+/**
+ * Checks a word for being a reserved word and returns true if the provided
+ * identifier string is a reserved word in some ECMAScript dialect.
+ *
+ * @param word word to check
+ * @param dialect dialect or version
+ * @param strict strict mode additionally checks whether word is a keyword or
+ * future reserved word under strict mode.
+ */
+export function check(
+    word: string,
+    dialect?: Dialect,
+    strict?: boolean
+): boolean;

types/reserved-words/reserved-words-tests.ts

@@ -0,0 +1,24 @@
+import { check, Dialect, KEYWORDS } from "reserved-words";
+
+const dialect: Dialect = "es3";
+
+// $ExpectType boolean
+check("while");
+
+// $ExpectType boolean
+check("while", "es6");
+
+// $ExpectType boolean
+check("while", "es6", true);
+
+// $ExpectType boolean
+check("yield", 3);
+
+// $ExpectError
+check("yield", 1);
+
+// $ExpectError
+check("yield", "es4");
+
+// $ExpectType true
+KEYWORDS["6-strict"]["break"];

types/reserved-words/tsconfig.json

@@ -0,0 +1,23 @@
+{
+    "compilerOptions": {
+        "module": "commonjs",
+        "lib": [
+            "es6"
+        ],
+        "noImplicitAny": true,
+        "noImplicitThis": true,
+        "strictNullChecks": true,
+        "baseUrl": "../",
+        "typeRoots": [
+            "../"
+        ],
+        "types": [],
+        "noEmit": true,
+        "forceConsistentCasingInFileNames": true,
+        "strictFunctionTypes": true
+    },
+    "files": [
+        "index.d.ts",
+        "reserved-words-tests.ts"
+    ]
+}

types/reserved-words/tslint.json

@@ -0,0 +1 @@
+{ "extends": "dtslint/dt.json" }