Complex sentence: The language grew out of a personal project by lead developer Graydon Hoare, who began work on it in 2006; his employer Mozilla became involved in 2009 and officially unveiled it for the first time in 2010.
Split into simpler sentences: The language grew out of a personal project by Mozilla employee Graydon Hoare. Mozilla began sponsoring the project in 2009 and announced it for the first time in 2010.