initial commit

js/goog/labs/useragent/useragent.js

@@ -0,0 +1,39 @@
+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Defines for goog.labs.userAgent.
+ */
+
+goog.module('goog.labs.userAgent');
+
+/**
+ * @define {string} Optional runtime override for the USE_CLIENT_HINTS flag.
+ * If this is set (for example, to 'foo.bar') then any value of USE_CLIENT_HINTS
+ * will be overridden by `globalThis.foo.bar` if it is non-null.
+ * This flag will be removed in December 2021.
+ */
+const USE_CLIENT_HINTS_OVERRIDE =
+    goog.define('goog.labs.userAgent.USE_CLIENT_HINTS_OVERRIDE', '');
+
+/**
+ * @define {boolean} If true, use navigator.userAgentData
+ * TODO(user) Flip flag in 2021/12.
+ */
+const USE_CLIENT_HINTS =
+    goog.define('goog.labs.userAgent.USE_CLIENT_HINTS', false);
+
+// TODO(user): Replace the IIFE with a simple null-coalescing operator.
+// NOTE: This can't be done with a helper function, or else we risk an inlining
+// back-off causing a huge code size regression if a non-inlined helper function
+// prevents the optimizer from detecting the (possibly large) dead code paths.
+/** @const {boolean} */
+exports.USE_CLIENT_HINTS = (() => {
+  const override = USE_CLIENT_HINTS_OVERRIDE ?
+         goog.getObjectByName(USE_CLIENT_HINTS_OVERRIDE) :
+         null;
+  return override != null ? override : USE_CLIENT_HINTS;
+})();