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2026-06-25 21:30:32 +00:00
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+/**
+ * @license
+ * Copyright The Closure Library Authors.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @fileoverview Browser capability checks for the events package.
+ */
+
+goog.module('goog.events.BrowserFeature');
+goog.module.declareLegacyNamespace();
+
+
+/**
+ * Tricks Closure Compiler into believing that a function is pure.  The compiler
+ * assumes that any `valueOf` function is pure, without analyzing its contents.
+ *
+ * @param {function(): T} fn
+ * @return {T}
+ * @template T
+ */
+const purify = (fn) => {
+  return ({valueOf: fn}).valueOf();
+};
+
+
+/**
+ * Enum of browser capabilities.
+ * @enum {boolean}
+ */
+exports = {
+  /**
+   * Whether the button attribute of the event is W3C compliant.  False in
+   * Internet Explorer prior to version 9; document-version dependent.
+   */
+  HAS_W3C_BUTTON: true,
+
+  /**
+   * Whether the browser supports full W3C event model.
+   */
+  HAS_W3C_EVENT_SUPPORT: true,
+
+  /**
+   * To prevent default in IE7-8 for certain keydown events we need set the
+   * keyCode to -1.
+   */
+  SET_KEY_CODE_TO_PREVENT_DEFAULT: false,
+
+  /**
+   * Whether the `navigator.onLine` property is supported.
+   */
+  HAS_NAVIGATOR_ONLINE_PROPERTY: true,
+
+  /**
+   * Whether HTML5 network online/offline events are supported.
+   */
+  HAS_HTML5_NETWORK_EVENT_SUPPORT: true,
+
+  /**
+   * Whether HTML5 network events fire on document.body, or otherwise the
+   * window.
+   */
+  HTML5_NETWORK_EVENTS_FIRE_ON_BODY: false,
+
+  /**
+   * Whether touch is enabled in the browser.
+   */
+  TOUCH_ENABLED:
+      ('ontouchstart' in goog.global ||
+       !!(goog.global['document'] && document.documentElement &&
+          'ontouchstart' in document.documentElement) ||
+       // IE10 uses non-standard touch events, so it has a different check.
+       !!(goog.global['navigator'] &&
+          (goog.global['navigator']['maxTouchPoints'] ||
+           goog.global['navigator']['msMaxTouchPoints']))),
+
+  /**
+   * Whether addEventListener supports W3C standard pointer events.
+   * http://www.w3.org/TR/pointerevents/
+   */
+  POINTER_EVENTS: ('PointerEvent' in goog.global),
+
+  /**
+   * Whether addEventListener supports MSPointer events (only used in IE10).
+   * http://msdn.microsoft.com/en-us/library/ie/hh772103(v=vs.85).aspx
+   * http://msdn.microsoft.com/library/hh673557(v=vs.85).aspx
+   */
+  MSPOINTER_EVENTS:
+      ('MSPointerEvent' in goog.global &&
+       !!(goog.global['navigator'] &&
+          goog.global['navigator']['msPointerEnabled'])),
+
+  /**
+   * Whether addEventListener supports {passive: true}.
+   * https://developers.google.com/web/updates/2016/06/passive-event-listeners
+   */
+  PASSIVE_EVENTS: purify(function() {
+    // If we're in a web worker or other custom environment, we can't tell.
+    if (!goog.global.addEventListener || !Object.defineProperty) {  // IE 8
+      return false;
+    }
+
+    var passive = false;
+    var options = Object.defineProperty({}, 'passive', {
+      get: function() {
+        passive = true;
+      }
+    });
+    try {
+      goog.global.addEventListener('test', goog.nullFunction, options);
+      goog.global.removeEventListener('test', goog.nullFunction, options);
+    } catch (e) {
+    }
+
+    return passive;
+  })
+};