startApp in not defined in Framework7

[jpacol]

Encountering this concern that startApp is not defined. I am using Framework7 and Cordova.

On my index.html, I have the following line.
<a href="#" data-href="" id="appTwitter"></a>

On my app.js, I have the following lines.
$$('#appTwitter').on('click', function () { startApp.set({ "application": "com.twitter.android" }).start(); });

But the result is: