events.js 2.2 KB

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  1. /**
  2. * @license
  3. * Copyright 2019 Google Inc.
  4. *
  5. * Permission is hereby granted, free of charge, to any person obtaining a copy
  6. * of this software and associated documentation files (the "Software"), to deal
  7. * in the Software without restriction, including without limitation the rights
  8. * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  9. * copies of the Software, and to permit persons to whom the Software is
  10. * furnished to do so, subject to the following conditions:
  11. *
  12. * The above copyright notice and this permission notice shall be included in
  13. * all copies or substantial portions of the Software.
  14. *
  15. * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16. * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17. * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  18. * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19. * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  20. * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  21. * THE SOFTWARE.
  22. */
  23. /**
  24. * Determine whether the current browser supports passive event listeners, and
  25. * if so, use them.
  26. */
  27. export function applyPassive(globalObj) {
  28. if (globalObj === void 0) { globalObj = window; }
  29. return supportsPassiveOption(globalObj) ?
  30. { passive: true } :
  31. false;
  32. }
  33. function supportsPassiveOption(globalObj) {
  34. if (globalObj === void 0) { globalObj = window; }
  35. // See
  36. // https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener
  37. var passiveSupported = false;
  38. try {
  39. var options = {
  40. // This function will be called when the browser
  41. // attempts to access the passive property.
  42. get passive() {
  43. passiveSupported = true;
  44. return false;
  45. }
  46. };
  47. var handler = function () { };
  48. globalObj.document.addEventListener('test', handler, options);
  49. globalObj.document.removeEventListener('test', handler, options);
  50. }
  51. catch (err) {
  52. passiveSupported = false;
  53. }
  54. return passiveSupported;
  55. }
  56. //# sourceMappingURL=events.js.map