Question

Probably a simple one but my knowledge of creating regular expressions is a little vague.

I’m trying to match any string followed by a comma and a space except if it is ‘Bair Hugger’ or ‘Fluid Warmer’

Here is what I have so far

var re_comma = new RegExp("\w+[^Bair Hugger|Fluid Warmer]" + ", ", "i");

Any ideas?

Answer 1

New answer

Regarding your example I’d say it is really easier to split the string and iterate over it:

function filter(str, delim, test) {
    var parts = str.split(delim),
        result = [];

    for(var i = 0, len = parts.length; i < len; i++) {
        if(test(parts[i])) result.push(parts[i]);
    }

    return result.join(delim);
}

str = filter(str, ', ', function(s) {
    s = s.toLowerCase();
    return s === 'bair hugger' || s === 'fluid warmer';
});

Otherwise, your expression becomes something like this:

new RegExp("(^|, )(?!(?:Bair Hugger|Fluid Warmer)(?:$|, )).+?(, |$)", "i");

and you have to use a callback for the replacement to decide whether to remove the preceding , or trailing , or not:

str = str.replace(re_comma, function(str, pre, tail) {
    return pre && tail ? tail : '';// middle of the string, leave one
});

The intention of this code is less clear. Maybe there is a simpler expression, but I think filtering the array is still cleaner.

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Old answer: (doesn’t solve the problem at hand but provides information regarding regular expressions).

[] denotes a character class and will only match one character out of the ones you provided. [^Bair Hugger|Fluid Warmer] is the same as [^Bair Huge|FldWm].

You could use a negative lookahead:

new RegExp("^(?!(Bair Hugger|Fluid Warmer), ).+?, $", "i");

Note that you have to use \\ inside a string to produce one \. Otherwise, "\w" becomes w and is not a special character sequence anymore.You also have to anchor the expression.

Update: As you mentioned you want to match any string before the comma, I decided to use . instead of \w, to match any character.