Restricting Character length in Regular expression

I am using the following regular expression without restricting any character length

var test =  /^(a-z|A-Z|0-9)*[^$%^&*;:,<>?()\""\']*$/ //Works Fine

In above when I am trying to restrict the characters length to 15 as below, it throws an error.

var test =  /^(a-z|A-Z|0-9)*[^$%^&*;:,<>?()\""\']*${1,15}/    //**Uncaught SyntaxError: Invalid regular expression**

Please help me to make the above regEx work with the characters limit to 15.



You cannot apply quantifiers to anchors. Instead, to restrict the length of the input string, use a lookahead anchored at the beginning:


Also, I assume you wanted to match 0 or more letters or digits with (a-z|A-Z|0-9)*. It should look like [a-zA-Z0-9]* (i.e. use a character class here).

Why not use a limiting quantifier, like {1,15}, at the end?

Quantifiers are only applied to the subpattern to the left, be it a group or a character class, or a literal symbol. Thus, ^[a-zA-Z0-9]*[^$%^&*;:,<>?()\"']{1,15}$ will effectively restrict the length of the second character class [^$%^&*;:,<>?()\"'] to 1 to 15 characters. The ^(?:[a-zA-Z0-9]*[^$%^&*;:,<>?()\"']*){1,15}$ will "restrict" the sequence of 2 subpatterns of unlimited length (as the * (and +, too) can match unlimited number of characters) to 1 to 15 times, and we still do not restrict the length of the whole input string.

How does the lookahead restriction work?

The (?=.{1,15}$) positive lookahead appears right after ^ start-of-string anchor. It is a zero-width assertion that only returns true or false after checking if its subpattern matches the subsequent characters. So, this lookahead tries to match any 1 to 15 (due to the limiting quantifier {1,15}) characters but a newline right at the end of the string (due to the $ anchor). If we remove the $ anchor from the lookahead, the lookahead will only require the string to contain 1 to 15 characters, but the total string length can be any.

If the input string can contain a newline sequence, you should use [\s\S] portable any-character regex construct (it will work in JS and other common regex flavors):



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