JavaScript: The Definitive Guide, Fourth Edition

The RegExp Object

As mentioned at the beginning of this chapter, regular expressions are represented as RegExp objects. In addition to the RegExp( ) constructor, RegExp objects support three methods and a number of properties. An unusual feature of the RegExp class is that it defines both class (or static) properties and instance properties. That is, it defines global properties that belong to the RegExp( ) constructor as well as other properties that belong to individual RegExp objects. RegExp pattern-matching methods and properties are described in the next two sections.

The RegExp( ) constructor takes one or two string arguments and creates a new RegExp object. The first argument to this constructor is a string that contains the body of the regular expression -- the text that would appear within slashes in a regular expression literal. Note that both string literals and regular expressions use the \ character for escape sequences, so when you pass a regular expression to RegExp( ) as a string literal, you must replace each \ character with \\. The second argument to RegExp( ) is optional. If supplied, it indicates the regular expression flags. It should be g, i, m, or a combination of those letters. For example:

// Find all five digit numbers in a string. Note the double \\ in this case.
var zipcode = new RegExp("\\d{5}", "g");

The RegExp( ) constructor is useful when a regular expression is being dynamically created and thus cannot be represented with the regular expression ...