SyntaxError: invalid range in character class

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.

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#

{{jsxref("SyntaxError")}}

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#

```js example-bad /[9-1]/; // The range is out of order /[_-=]/; // _ has value 95, = has value 61

### Valid cases

```js example-good
/[1-9]/; // Swap the range
/[_\-=]/; // Escape the hyphen so it matches the literal character

See also#

• Regular expressions
• Character class: [...], [^...]