In April of 2010, Steve Jobs penned an open letter titled "Thoughts on Flash" in which he stated the "new open standards created in the mobile era, such as HTML5, will win". Facebook seemingly later validated Jobs’ thought when rumor came of a major initiative called Project Spartan that would make Facebook apps completely based on HTML5.
HTML5 was the next big thing. The unifier. The Holy Grail. Code once, it works everywhere. That was the promise