javascript - Replace part of string that doesn't match regex

Question

I am attempting to replace parts of a string that don't match a regular expression pattern using JavaScript. This is functionally equivalent to using the -v flag in a GNU grep to invert results. Here is an example:

// I want to replace all characters that don't match "fore" 
// in "aforementioned" with "*"

'aforementioned'.replace(new RegExp(pattern, 'i'), function(match){
    //generates a string of '*' that is the length of match
    return new Array(match.length).join('*');
});

I am looking for a regex for pattern. This would be something like the opposite of (fore). I've searched around but haven't been able to implement any related question's answers to fit my needs. Here is a list anyway, maybe it will point us in the right direction:

• Regular Expressions and negating a whole character group
• Match everything except for specified strings

Answer 1

If I understand you correctly, this should be one possible solution:

'aforementioned'.replace(new RegExp(pattern + '|.', 'gi'), function(c) {
    return c === pattern ? c : '*';
});

>> "*fore*********"