匹配以特殊字符开头或结尾的整个单词

Question

I need a regular expression in javascript that matches whole words that start or end with special characters?

It was supposed to be easy, but for some reason \\b after ? doesn't behave as I expected:

> /FOO\?/.exec('FOO? ')
[ 'FOO?', index: 0, input: 'FOO? ', groups: undefined ]
> /FOO\?\b/.exec('FOO? ')
null

What I need, for instance if my word is "FOO?" (including the question mark), I want to match:

"FOO? is cool", "do you think that FOO??"

but not: "FOO is cool", "FOO?is cool", "aaFOO?is cool"

It should also work for words that start with "?". For instance, if my word if "?FOO", I want to match:

"?FOO is cool", "I love ?FOO"

but not: "FOO is cool", "FOO?is cool", "aaFOO?is cool"

I hope it makes sense.

Answer 1

The \\b word boundary construct is ambiguous. You need to use unambiguous constructs that will make sure there are non-word chars or start/end of string to the left/right of the word matched.

You may use

/(?:^|\W)\?FOO\?(?!\w)/g

Here, (?:^|\\W) is a non-capturing group that matches either the start of a string or any non-word char, a char other than an ASCII letter, digit and _ . (?!\\w) is a negative lookahead that fails the match if, immediately to the right of the current location, there is a word char.

Or, with ECMAScript 2018 compatible JS environments,

/(?<!\w)\?FOO\?(?!\w)/g

See this regex demo .

The (?<!\\w) is a negative lookbehind that fails the match if there is a word char immediately to the left of the current location.

In code, you may use it directly with String#match to extract all occurrences, like s.match(/(?<!\\w)\\?FOO\\?(?!\\w)/g) .

The first expression needs a capturing group around the word you need to extract:

 var strs = ["?FOO is cool", "I love ?FOO", "FOO is cool", "FOO?is cool", "aaFOO?is cool"]; var rx = /(?:^|\\W)(\\?FOO)(?!\\w)/g; for (var s of strs) { var res = [], m; while (m=rx.exec(s)) { res.push(m[1]); } console.log(s, "=>", res); }