Which came first, JavaScript or YouTube?

JavaScript came first, by 10 years. Brendan Eich wrote it in ten days for Netscape Navigator.

Side by side

JavaScript

JavaScript was written in about ten days in May 1995, shipped in Netscape Navigator 2.0 later that year, and was called LiveScript until December, when Netscape renamed it as part of a marketing deal with Sun. It has nothing to do with Java beyond some borrowed syntax. Standardisation as ECMAScript followed in 1997, and the language spent a decade being treated as a toy before it became the most widely deployed programming language in the world.

YouTube

The youtube.com domain was registered on Valentine's Day 2005, the first video — "Me at the zoo", 19 seconds of a co-founder at San Diego Zoo — was uploaded on 23 April, and the site opened publicly in the winter. Google bought it in November 2006 for $1.65 billion, about twenty months after the domain was registered. It is younger than Facebook by a year and older than Twitter by one.