I have this function that checks if the entered Url is valid.
The problem is that I also need to know if this Url comes from facebook.com or not.
If not the Url should not be considered as valid.
How do I edit the function below to make it expects an Url with facebook.com string inside?

```
function isUrl(s) {

var regexp = /(ftp|http|https):\/\/(\w+:{0,1}\w*@)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%@!\-\/]))?/
return regexp.test(s);
}

```