JavaScript function that returns AJAX call data

I would like to create a JavaScript function which returns the value of a jQuery AJAX call. I would like something like this.

function checkUserIdExists(userid){
    return $.ajax({
        url: 'theurl',
        type: 'GET',
        cache: false,
        data: {
           userid: userid
        },
        success: function(data){
            return data;
        }
    });
}

I know I can do this by setting async to false but I would rather not.