The Year 19100

The JavaScript Y2K bug. getYear() returned 99 in 1999, so pages printed the century themselves. Then the year 100 arrived.

In 2026: Still works, which is the joke: getYear() survives in the compatibility annex of the JavaScript spec and still returns the year minus 1900, so the demo below glues 19 in front of that number and prints a four digit year wrong by a century. On the first of January 2000, half the web's footers read 19100. getFullYear() had already shipped two years earlier, in browsers nobody had upgraded.

Where it came from: JavaScript 1.0 Date.getYear, Netscape 2, 1996. The fix, getFullYear, shipped in 1998 and plenty of pages ignored it. MDN ↗

<script language="JavaScript">
var today = new Date();
// getYear() returns the year minus 1900. In 1998 that was "98",
// so everyone just glued "19" in front of it.
document.write("Copyright 19" + today.getYear() + ". All rights reserved.");
</script>