How to extract a number from this simple string using RegExp in JavaScript?

Question

I need to extract the number from the following simple string:

base:873

where the "base:" portion is optional, ie, it may/may not exist in the string.

How am I supposed to extract the number from the above string using RegExp?

PS: It's an unfortunate to see such a big difference between other Regular Expression implementation and the JavaScript's one.

TIA, Mehdi

UPDATE1:

Consider this loop:

for (var i = 0; i < 3; i++) {
    code = '216';

    var matches = /(bid:)?(\d+)/ig.exec(code);
    if (matches != null) {
        console.log('>>>' + matches[0]);
    }
    else {
        console.log('>>> no match');
    }
}

Please note that the "code" variable is set within the loop, just for testing purposes only. However, the amazing thing is that the above mentioned code prints this:

>>>216
>>> no match
>>>216

How this could be possible???

Answer 1

Well, if the base: is optional, you don't need to care about it, do you?

\d+

is all you need.

result = subject.match(/\d+/);

will return the (first) number in the string subject .

Or did you mean: Match the number only if it is either the only thing in the string, or if it is preceded by base: ?

In this case, use ^(?:base:)?(\\d+)$ .

var match = /^(?:base:)?(\d+)$/.exec(subject);
if (match != null) {
    result = match[1];
}

Answer 2

Try (base:)?(\\d+)

The number will be in the second capture variable.

Alternately, replace "base:" with nothing.

Or split on the ':'.

Or whatever.