Unable to reference variable inside animate method

Unable to reference variable inside animate method

I have the following function: 

$("#scroll1").click(function () {
    var scrollId = $(this).attr("id");
    $('html, body').animate({
        scrollTop: ($(scrollId).offset().top-100)
    }, 500);
})

When this fires I get:  Uncaught TypeError: Cannot read property 'top' of undefined

This is on my variable reference in scrollTop: ($(scrollId).offset().top-100)

How can I reference the scrollId variable inside my .animate?