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// from swr import isBrowser from '../../../utils/isBrowser'; import isDocumentVisible from './isDocumentVisible'; import isOnline from './isOnline'; var listeners = []; function subscribe(listener) { listeners.push(listener); return function unsubscribe() { var index = listeners.indexOf(listener); if (index > -1) { listeners.splice(index, 1); } }; } if (isBrowser) { var revalidate = function () { if (!isDocumentVisible() || !isOnline()) return; for (var i = 0; i < listeners.length; i++) { var listener = listeners[i]; listener(); } }; window.addEventListener('visibilitychange', revalidate, false); window.addEventListener('focus', revalidate, false); } export default subscribe;