Google Maps was released in 2006, and it was not the first "single-page app". XmlHTTPRequest was invented at Microsoft for Outlook's browser-based client in 1999, and Mozilla had a compatible copy by 2000. The original iPhone was released in 2007 without 3rd party native apps or an App Store, pushing devs to build HTML5 apps instead. Even small consulting firms like the ones I worked at at the time we very interested in JS to "prevent screen flicker" (aka page reload in MBA speak).

I think it's a major stretch to say JS wasn't taken seriously 10 years ago.