Fetching A GET URL

in PHP you can make a statement to the likes of

if (issett($_GET)) {
do stuff
}
else {
do other stuff
}

I was wondering what the equivalent is to call a GET with javascript EXAMPLE

<a href="page=yourpage&action=edit">edit</a>

<a href="page=yourpage&action=add">Add</a>

consider those 2 URL's

the JS:

if (action=edit) {
do this;
}
else if (action = add){
do something else;
}