W3schools. (s.f.). HTML DOM getElementById() Method. Recuperado de http://www.w3schools.com/jsref/met_document_getelementbyid.asp

W3schools. (s.f.). onclick Event. Recuperado de http://www.w3schools.com/jsref/event_onclick.asp

W3schools. (s.f.). HTML DOM textContent Property. Recuperado de http://www.w3schools.com/jsref/prop_node_textcontent.asp