The RegExp().compile() method is deprecated. It’s basically the same as the constructor, which I assume is why it was deprecated. You should only have to use the constructor nowadays.
In other words, you used to be able to do this:
var regexp = new RegExp("pattern");
regexp.compile("new pattern");
But nowadays it is not any different from simply calling:
var regexp = new RegExp("pattern");
regexp = new RegExp("new pattern");