Question

I am stuck with a little regular expression
I am trying to match every substring that start with a given prefix using regular expression
in javascript

prefix = "pre-"
regex = /???/

"pre-foo-bar bar pre-bar barfoo".replace(regex, '')
// should output "bar barfoo"

Answer 1

/\bpre-\S*\s?/g works, assuming you want to strip out the trailing space as well (per your example). If you want to leave it in, use /\bpre-\S*/g

Correction

\b only looks up word characters, and - is definitely not a word character. Unfortunately, JavaScript doesn’t support custom lookbehinds.

/(\s|^)pre-\S*/g should work, but there will be a leading space compared to the example output given above. This checks for “pre-” preceded either by nothing or a space character and then followed by 0 or more non-space characters. It removes the whole block except the space. If the space is really important to you, you could do:

str.replace(/(\s|^)pre-\S*\s?/g, function(wholeString, optionalSpaceCharacter) {
    return optionalSpaceCharacter;
});

Second Correction

The complex replace I gave you won’t work if you have two in a row like, “pre-a pre-b pre-c”. You’ll end up with "pre-b " because of the \s? at the end. Your best bet to get the exact desired output is to use /(\s|^)pre-\S*/g and check the original string if it started with “pre-” if so, just remove one space from the beginning.

str.replace(/(\s|^)pre-\S*/g, '').substring(str.substring(0, 4) == "pre-" ? 1 : 0);