"invalid range in character class": JavaScript Error Solved

"invalid range in character class"

It was maddening. Firebug showed this error, but gave no additional information: not even a script or function name, much less a line number. Googling didn't help very much: it suggested that it was an error involving regular expressions. Thousands and thousands of lines of code and at least half a dozen external JavaScript files later, I'm pleased to say that I discovered what the message means and now want to pass along the knowledge in hopes of saving someone else endless hours.

The short answer is that the word range refers to a "range of values," say the range from 1 to 100 typically written as 1-100. Notice that my shorthand for range involves a dash or minus sign between the 1 and 100. Therein lies the problem. If you want a regular expression to test for the presence of a dash/minus sign as a dash/minus sign, it needs to be escaped with a backslash, or else some browsers (Firefox 2 in this case) think that you are attempting to express a range instead and freak out accordingly.

In particular, I had one tiny function that was used on only one form dealing with phone numbers. Valid data included a blank space, any number, a dash, or a right or left parenthesis to accommodate a number such as (555) 555-5555. It wasn't crucial that users type in their phone number in any certain way, I just try to get in the practice of filtering my data both client and server side.

In a test copy of the production environment, I first eliminated my scripts one by one until the offending error disappeared. Then I brought that script back, eliminating each function body until the error disappeared. It turned out to be this tiny function, short for "is integer" though obviously adding the space, dash, and parentheses:

var isInt = function(s) {
    s.value = s.value.replace(/[^\d-()\s]+/g, '');
};

Notice that the - character is not escaped. Now here's the fix:

var isInt = function(s) {
    s.value = s.value.replace(/[^\d\-()\s]+/g, '');
};

I have now added the escape \-, and thousands of lines of code are now working again. Hopefully this post will save someone else hours of frustration.

Update: As Earl suggests in his comment below, you can also move the dash to the end of your regular expression square brackets without using an escape: /[^\d()\s-]+/g. 5n1p3r also brings up the point below that if you're using the RegExp object and an escape, you need two backslashes, the first to escape your escape.