How to do case insensitive string comparison?

How do I perform case insensitive string comparison in JavaScript?

EDIT: This answer was originally added over 10 years ago. Today should use localeCompare. See the other answers.

The simplest way to do it (if you're not worried about special Unicode characters) is to call toUpperCase:

var areEqual = string1.toUpperCase() === string2.toUpperCase();

Stack Overflow Q#2140627, score: 1550