Javascript replace with reference to matched group?

I have a string, such as hello _there_. I'd like to replace the two underscores with <div> and </div> respectively, using JavaScript. The output would (therefore) look like hello <div>there</div>. The string might contain multiple pairs of underscores.

What I am looking for is a way to either run a function on each match, the way Ruby does it:

"hello _there_".gsub(/_.*?_/) { |m| "<div>" + m[1..-2] + "</div>" }

Or be able to reference a matched group, again the way it can be done in ruby:

"hello _there_".gsub(/_(.*?)_/, "<div>\\1</div>")

Any ideas or suggestions?

"hello _there_".replace(/_(.*?)_/, function(a, b){
    return '<div>' + b + '</div>';
})

Oh, or you could also:

"hello _there_".replace(/_(.*?)_/, "<div>$1</div>")

EDIT by Liran H: For six other people including myself, $1 did not work, whereas \1 did.

You can use replace instead of gsub.

"hello _there_".replace(/_(.*?)_/g, "<div>\$1</div>")