// The function actually applying the offset
function offsetAnchor() {
if(location.hash.length !== 0) {
window.scrollTo(window.scrollX, window.scrollY - 100);
}
}
// This will capture hash changes while on the page
window.addEventListener("hashchange", offsetAnchor);
// This is here so that when you enter the page with a hash,
// it can provide the offset in that case too. Having a timeout
// seems necessary to allow the browser to jump to the anchor first.
window.setTimeout(offsetAnchor, 1); // The delay of 1 is arbitrary and may not always work right (although it did in my testing).