Toggling OS X Sound Output Devices with JXA Javascript for Automation (OS X 10.10)

soundDeviceToggle.js

// Rob Trew @complexpoint 2015
function run() {
	"use strict";

	var blnUseKeyboardMaestro = false;

	// EDIT TO NAMES OF TWO ALTERNATIVE SOUND OUTPUT DEVICES
	var dctSources = { // A unique substring for each is enough
		primary: "Internal",
		secondary: "Elgato"
	}

	if (blnUseKeyboardMaestro) {
		// NB if you are using KeyBoard Maestro, the values of the KM variables,

		var strVarNameONE = "soundDeviceONE"
		var strVarNameTWO = "soundDeviceTWO"

		//  take precedence (as long as they are both set, 
		//	and different from the strings above)

		//  Otherwise, [blnUseKeyboardMaestro = false] 
		//  the dctSources setting above will be used

		var oPrimary = findOrMakeKMVar(strVarNameONE),
			oSecondary = findOrMakeKMVar(strVarNameTWO),
			kmvarPrimary = oPrimary.value(),
			kmvarSecondary = oSecondary.value();

		if (kmvarPrimary) dctSources.primary = kmvarPrimary;
		else oPrimary.value = dctSources.primary;

		if (kmvarSecondary) dctSources.secondary = kmvarSecondary;
		else oSecondary.value = dctSources.secondary;
	}


	// ASSUMING / CREATING TWO KEYBOARD MAESTRO VARIABLES
	// Get a reference to a Keyboard Maestro variable
	function findOrMakeKMVar(strName) {
		var appKM = Application("Keyboard Maestro Engine"),
			oVars = appKM.variables;

		try {
			oVars[strName].name();
		} catch (e) {
			oVars.push(appKM.Variable({
				'name': strName
			}));
		}
		return oVars[strName];
	}

	var appPrefs = Application("System Preferences"),
		blnFound = false,
		strLegend, strMsg;

	// FIND SOUND TAB OF SYS PREFS
	appPrefs.panes[
		"com.apple.preference.sound"
		].anchors["output"].reveal();

	// FIND CURRENT DEVICE SELECTION
	var rows = Application("System Events").processes[
			"System Preferences"
			].windows[0].tabGroups[0].scrollAreas[0].tables[0].rows,
		strSeln = rows.where({
			"selected": true
		})[0].textFields[0].value();

	// CHOOSE NEW TARGET BY TOGGLING
	var strTarget = (strSeln.indexOf(dctSources.primary) !== -1) ?
		dctSources.secondary :
		dctSources.primary;

	// FIND AND AND SELECT THE FIRST MATCHING LINE
	rows().forEach(function (oRow) {
		if (!blnFound) {
			strLegend = oRow.textFields[0].value();
			if (strLegend.indexOf(strTarget) !== -1) {
				oRow.select();
				blnFound = true;
			}
		}
	});

	// NOTIFY FAILURE OR NEW SETTING
	var app = Application.currentApplication();
	app.includeStandardAdditions = true;
	app.activate();
	app.displayNotification(
		blnFound ?
		"→ " + strLegend :
		"Couldn't find a sound device containing this string: \"" + strTarget +
		'\"', {
			withTitle: "Sound Output Device " +
				(blnFound ? '' : 'NOT ') + "Changed"
		}
	);
	
	// AND TIDY UP
	appPrefs.quit();
	return blnFound;
}