1995
JavaScript, when a language built in 10 days changed the world
"Type something wrong in the form and a red message pops up right there!" One engineer threw together a temporary little language in ten days, and it ended up as the bloodstream of Facebook, Toss, and KakaoTalk.
Until 1995, every web page was as static as a sheet of paper. HTML could show text and images, and that was it. If a user typed something into a form, processing it was strictly the server's job. Want to see "this isn't a valid email address" on a signup form? You clicked submit, the browser sent the data, the server checked it, the server sent back a whole new page, and the browser repainted everything from scratch. A single validation check could take five seconds.
A Netscape engineer named Brendan Eich stared at the problem and thought, "Wait — what if a tiny program could run inside the browser itself? Something simple like checking an email format wouldn't have to make a round trip to the server. The browser could just handle it on the spot."
In just ten days he sketched out a brand-new programming language and shipped it inside Netscape Navigator. He called it JavaScript (similarly named to Java but, in fact, an entirely different language). The first user to try it was thrilled: "I typed something invalid and a red error message appeared right there, instantly! I didn't have to reload anything!" A simple form check was the modest beginning, but it would quietly rewrite the future of the web.
Today, JavaScript is the most widely used programming language on Earth. Facebook, Instagram, Gmail, YouTube, X, Discord — every site you touch in a day is built on top of it. A throwaway language one engineer wrote in ten days became the bloodstream of the internet. He almost certainly didn't expect that "let's just hack something together because we need it" would still be powering the world thirty years later.
JavaScript introduced the event loop, dynamic typing, and DOM scripting—capabilities that defined the browser as an application runtime.