Javascript regex invalid range in character class

Question

I\'m using a regex pattern that I got from regexlib to validate relative urls. On their site you can test the pattern to make sure it fits your needs. Everything works great

Answer 1

There is no reason to use RegExp constructor here. Just use RegExp literal:

var urlRegex = /^(?:(?:\.\.\/)|\/)?(?:\w(?:[\w`~!$=;\-\+\.\^\(\)\|\{\}\[\]]|(?:%\d\d))*\w?)?(?:\/\w(?:[\w`~!$=;\-\+\.\^\(\)\|\{\}\[\]]|(?:%\d\d))*\w?)*(?:\?[^#]+)?(?:#[a-z0-9]\w*)?$/g;
               ^           ^   ^                                                               ^                                                                                     ^

Inside RegExp literal, you just write the regex naturally, except for /, which now needs escaping, since / is used as delimiter in the RegExp literal.

In character class, ^ has special meaning at the beginning of the character class, - has special meaning in between 2 characters, and \ has special meaning, which is to escape other characters (mainly ^, -, [, ] and \) and also to specify shorthand character classes (\d, \s, \w, ...). [, ] are used as delimiters for character class, so they also have special meaning. (Actually, in JavaScript, only ] has special meaning, and you can specify [ without escaping inside character class). Other than those 5 character listed above, other characters (unless involved in an escape sequence with \) doesn't have any special meaning.

You can reduce the number of escaping \ with the information above. For ^, unless it is the only character in the character class, you can put it away from the beginning of the character class. For -, you can put it at the end of the character class.

var urlRegex = /^(?:(?:\.\.\/)|\/)?(?:\w(?:[\w`~!$=;+.^()|{}\[\]-]|(?:%\d\d))*\w?)?(?:\/\w(?:[\w`~!$=;+.^()|{}\[\]-]|(?:%\d\d))*\w?)*(?:\?[^#]+)?(?:#[a-z0-9]\w*)?$/g;

What was changed:

[\w`~!$=;\-\+\.\^\(\)\|\{\}\[\]]
[\w`~!$=;+.^()|{}\[\]-]

Answer 2

Either put - at the end or beginning of the character class or use two backslashes to do a regex escape within string

since you are using string you need to use two backslashes for each special characters..

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NOTE

Check out this answer on SO which explains when to use single or double backslashes to escape special characters