Regular expressions are a way of describing a pattern match that can be used to select a group of characters from an input string. This usually then leads on to replacing them with some other set of characters. It is analogous to the find and replace capability in a word processor.
Regular expressions are managed by creating a RegExp object with the RegExp() constructor. RegExp objects support a literal syntax and can be created on the fly without needing a constructor call which makes them extremely convenient to deploy.
The ECMAScript standard ratifies regular expressions in the third edition. They were not present in the second edition.
Regular expressions are still an area of concern when developing portable content. For example, they are completely unsupported on the WebTV platform as of the Summer 2000 release of the JellyScript interpreter.