Which came first, Amazon or JavaScript?

Amazon came first, by one year. Jeff Bezos incorporated the company in Washington state.

Side by side

Amazon

Amazon was incorporated on 5 July 1994, originally as Cadabra, and the website opened in July 1995 selling only books. The 1994 incorporation date is used here because it is the company's own founding date; if you mean the shop, 1995 is the answer. Either way it predates Google by three or four years and eBay by about a year.

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.