Build: Restore strict mode compatibility

When bundling qunit as a library in another build, the use of `this`
would cause an error strict mode due to being undefined there.

Adopt [ES2020 globalThis](https://github.com/tc39/proposal-global),
and polyfill it for environments that don't implement it yet.

Fixes #1557.
Closes #1558.

lib/global-this-polyfill.js

@@ -0,0 +1,49 @@
+/*
+https://github.com/ungap/global-this/blob/v0.4.4/esm/index.js
+
+Copyright (c) 2020, Andrea Giammarchi, @WebReflection
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
+
+-------
+
+Patches for use in QUnit:
+
+- 2021-02-25: Export as module only, don't change global scope as QUnit must not
+  affect the host context (e.g. people may test their application intentionally
+  with different or no polyfills and we must not affect that).
+
+*/
+
+let foundGlobalThis;
+
+(function (Object) {
+  if (typeof globalThis === "object") {
+    foundGlobalThis = globalThis;
+  } else {
+    this
+      ? get()
+      : (Object.defineProperty(Object.prototype, "_T_", {
+          configurable: true,
+          get: get,
+        }),
+        _T_);
+
+    function get() {
+      foundGlobalThis = this || self;
+      delete Object.prototype._T_;
+    }
+  }
+})(Object);
+
+export default foundGlobalThis;

rollup.config.js

@@ -40,10 +40,6 @@ module.exports = {
 				__dirname + "/src/html-reporter/es6-map.js",
 				"utf8"
 			).toString().trim();
-		},
-
-		globals: {
-			global: "(function() { return this; }())"
 		}
 	},
 	plugins: [
@@ -57,8 +53,5 @@ module.exports = {
 			babelHelpers: "bundled",
 			babelrc: true
 		} )
-	],
-	external: [
-		"global"
 	]
 };

src/export.js

@@ -1,6 +1,6 @@
 /* global module, exports, define */
 import { window, document, self } from "./globals";
-import global from "global";
+import globalThis from "../lib/global-this-polyfill";
 
 export default function exportQUnit( QUnit ) {
 	let exportedModule = false;
@@ -54,6 +54,6 @@ export default function exportQUnit( QUnit ) {
 	// For other environments, such as SpiderMonkey (mozjs) and other
 	// embedded JavaScript engines
 	if ( !exportedModule ) {
-		global.QUnit = QUnit;
+		globalThis.QUnit = QUnit;
 	}
 }

src/globals.js

@@ -1,20 +1,20 @@
-import global from "global";
+import globalThis from "../lib/global-this-polyfill";
 
-export const window = global.window;
-export const self = global.self;
-export const console = global.console;
-export const setTimeout = global.setTimeout;
-export const clearTimeout = global.clearTimeout;
+export const window = globalThis.window;
+export const self = globalThis.self;
+export const console = globalThis.console;
+export const setTimeout = globalThis.setTimeout;
+export const clearTimeout = globalThis.clearTimeout;
 
 export const document = window && window.document;
 export const navigator = window && window.navigator;
 
 export const localSessionStorage = ( function() {
 	const x = "qunit-test-string";
 	try {
-		global.sessionStorage.setItem( x, x );
-		global.sessionStorage.removeItem( x );
-		return global.sessionStorage;
+		globalThis.sessionStorage.setItem( x, x );
+		globalThis.sessionStorage.removeItem( x );
+		return globalThis.sessionStorage;
 	} catch ( e ) {
 		return undefined;
 	}

src/test.js

@@ -1,5 +1,4 @@
-import global from "global";
-
+import globalThis from "../lib/global-this-polyfill";
 import { begin } from "./core";
 import { setTimeout, clearTimeout } from "./globals";
 import { emit } from "./events";
@@ -648,8 +647,8 @@ function saveGlobal() {
 	config.pollution = [];
 
 	if ( config.noglobals ) {
-		for ( const key in global ) {
-			if ( hasOwn.call( global, key ) ) {
+		for ( const key in globalThis ) {
+			if ( hasOwn.call( globalThis, key ) ) {
 
 				// In Opera sometimes DOM element ids show up here, ignore them
 				if ( /^qunit-test-output/.test( key ) ) {