unload.js

var MENU_ID = 'unload-tab';

var options = {
	'new-tab-placement': 'after',
	'page-context-menu': false,
};

console.log('loading', MENU_ID);

function option(item, values) {
	let opt = options[item];
	switch(typeof values) {
		case 'object':
			console.log("option", item, opt, values[opt]);
			return values[opt];
		case 'boolean':
			return opt ? values : value_if_false;
		case 'string':
			return values[opt];
		case 'undefined':
			console.error("Failed to load option", item, values, typeof values);
	}
}


function unloadTab(item, tab) {
	// Can't unload active tab.
	if(tab.active) {
		return browser.windows.get(tab.windowId, {populate: true}).then(window => {
			// adjust reframes index to be relative to tab
			function adjust(index) {
				return index < tab.index ? index + window.tabs.length : index;
			}

			var active = window.tabs
				// Filter discarded tabs and current tab.
				.filter(cur => !cur.discarded && cur.id != tab.id)
				// Pick next active window from ring relative to tab
				.reduce((acc, cur) => {
					if(acc === undefined) return cur;
					return adjust(cur.index) < adjust(acc.index) ? cur : acc;
				}, undefined);

			return active
				// Set the next tab to active
				? browser.tabs.update(active.id, {active: true})
				// Create a new tab if all are disabled. Set it active.
				: browser.tabs.create({
					active: true,
					index: option('new-tab-placement', {after: tab.index + 1, last: window.tabs.length}),
				});
		}, console.error).then(() => browser.tabs.discard(tab.id));
	} else {
		return browser.tabs.discard(tab.id);
	}
}

function load_options() {
	console.log("load_options");
	
	browser.storage.sync.get()
		.then(values => {
			Object.assign(options, values);
			if(Object.entries(values).length === 0) {
				return browser.storage.sync.set(options);
			}
			console.log('options loaded', options);
		})
		.catch(console.error)
		.finally(() => browser.storage.onChanged.addListener((changes, area) => {
			Object.keys(changes).forEach(key => {
				options[key] = changes[key].newValue;
				console.log('storage', area, 'change', key, changes[key]);
			})
			
			menu_update();
		}))
		.then(menu_create);
}

var menu_options = {
	id: MENU_ID,
	type: 'normal',
	title: 'Unload Tab',
	enabled: true,
	contexts: [],
	icons: null,
	onclick: unloadTab,
}
function menu_config() {
	menu_options.contexts = option('page-context-menu', {true: ['tab', 'page'], false: ['tab']});
}
function menu_create() {
	menu_config();
	
	browser.menus.create(menu_options, function() {
		if(browser.runtime.lastError) {
			console.error('Unload Tab: Error creating menu item. ' + browser.runtime.lastError);
		} else {
			console.log("Created menu");
		}
	});
	
	// Show/Hide entry based on unloaded state of tab
	browser.menus.onShown.addListener(function(item, tab) {

		// Update menu with status of tab
		browser.menus.update(MENU_ID, {
			enabled: !tab.discarded,
			visible: !(tab.url && tab.url.startsWith('about:')),
		});

		// Refresh menu to show changes
		browser.menus.refresh();
	});
}
function menu_update() {
	
	browser.menus.update(MENU_ID, {
		contexts: option('page-context-menu', {true: ['tab', 'page'], false: ['tab']}),
	});
}

load_options();