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So how are regular expressions implemented in Java Script? 2) When you need to dynamically construct the regular expression, via the The Reg Exp() method allows you to dynamically construct the search pattern as a string, and is useful when the pattern is not known ahead of time.Technical support for the Microsoft products and technologies referenced in this guidance is provided by Microsoft Support Services. It is provided as a courtesy for individuals who are still using these technologies.For support information, please visit the Microsoft Support Web site at To get the most benefit, find the newsgroup that corresponds to your technology or problem. This page may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist.Enclosing the expression in the caret (^) and dollar sign ($)markers ensures that the expression consists of the desired content and nothing else.A ^ matches the position at the beginning of the input string and a $ matches the position at the end of the input string.PERL programmers and UNIX shell programmers have enjoyed the benefits of regular expressions for years.