@bigfishtv/cockpit/src/utils/windowVisible.js

/**
 * Window Visible Utility
 * @module Utilities/windowVisible
 */

let stateKey = null
let eventKey = null

const keys = {
	hidden: 'visibilitychange',
	webkitHidden: 'webkitvisibilitychange',
	mozHidden: 'mozvisibilitychange',
	msHidden: 'msvisibilitychange',
}

for (stateKey in keys) {
	if (stateKey in document) {
		eventKey = keys[stateKey]
		break
	}
}

/**
 * Returns true/false if window is visible
 * @param  {Object} _window - defaults to window
 * @return {Boolean}
 */
export function windowVisible(_window = window) {
	return !_window.document[stateKey]
}

/**
 * Adds 'visibilitychange' listener to window and binds to provided callback
 * @param  {Function} callback
 * @param  {Object} _window - defaults to window
 * @return {Function}
 */
export function onVisibilityChange(callback, _window = window) {
	const func = () => callback(windowVisible(_window))
	_window.document.addEventListener(eventKey, func)
	return () => _window && _window.document && _window.document.removeEventListener(eventKey, func)
}