Javascript regular expression to match various strings

I have a question that I can't resolve. I have strings that contains hashtags, for example '开发者_开发技巧#question' or '#idea'.

The question is how extract the hashtag?

var hashtag = str.match(/#question?#idea?/i);

Is this regexp correct?

Your line

var hashtag = str.match(/#question?#idea?/i);

checks whether a string contains a literal #questio, optionally followed by n, followed by #ide, optionally followed by a. If that's the case, hashtag[0] will contain the matched text. This is obviously not what you want.

Try this:

// match a #, followed by either "question" or "idea"
var myregexp = /#(question|idea)\b/i;
var match = myregexp.exec(subject);
if (match != null) {
    result = match[1]; // will contain "question" or "idea"
} else {
    result = "";
}

The \b at the end of the regex is a word boundary anchor. It ensures that only #question but not #questionnaire will be matched.

If you don't know the names of the hashtags beforehand, use

var myregexp = /#(\w+)/;

(this allows ASCII letters, digits and underscore as possible hashtag characters - I don't know if those are the only valid characters. If not, you can use a character class. For example, to allow dashes, too:

var myregexp = /#([\w-]+)/;

No your regex is not correct.

/#question?#idea?/i

You search for each character in your regex, in this order. The ? makes the character before comes 0 or 1 times, the i at the end makes the expression ignoreCase, i.e. treat upper and lower case the same. You will find:

#question#idea
#questio#ide
#questio#idea
#QUEStion#IDea

but not

#question
#idea

Do you have a fixed set of tags, can they contain only letters, or also numbers, or other characters?

You can check your regexes e.g. here online My example

var str = "/foo=bar?#quesAion#dwdad";
var regi = new RegExp("(#[a-z0-9_-]*)", "gi");
var hashtag = str.match(regi);

Hashtag will be an array of found strings or null if not found any.