The JavaScript exception "invalid range in character class" occurs when a character class in a regular expression uses a range, but the start of the range is greater than the end.
SyntaxError: invalid range in character class
Message
SyntaxError: Invalid regular expression: /[2-1]/: Range out of order in character class (V8-based) SyntaxError: invalid range in character class (Firefox) SyntaxError: Invalid regular expression: range out of order in character class (Safari)
Error type
What went wrong?
In character classes, you can join two characters with a hyphen - to represent an inclusive interval of characters based on their Unicode code points. For example, [a-z] matches any lowercase letter. However, if the end of the range is less than the start, the range cannot match anything and is likely a mistake.
Examples
Invalid cases
/[9-1]/; // The range is out of order /[_-=]/; // _ has value 95, = has value 61
Valid cases
/[1-9]/; // Swap the range /[_\-=]/; // Escape the hyphen so it matches the literal character
See also
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https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Regex_invalid_range_in_character_class