When a regular expression is successfullyy matched against a target string, it is possible to extract the portions of the target string that matched any particular paranthesized subpattern. The essential purpose of parantheses in regular expressions is to define subpatterns within the complete pattern.
The method that performs the search-and-replace operation to strings for pattern matching is
The Crockford’s subset does not include the with and continue statements or the eval() function. It defines functions using function definition expressions only and does not include the function definition statement.
The subset does not include the comma operator, the bitwise operators, or the ++ and — operators. It also disallows == and != because of the type conversion they perform, requiring use of === and !== instead.