get document height js

1var body = document.body,
2    html = document.documentElement;
3
4var height = Math.max( body.scrollHeight, body.offsetHeight, 
5                       html.clientHeight, html.scrollHeight, html.offsetHeight );

1let body = document.body, html = document.documentElement, 
2    height = Math.max( body.scrollHeight, body.offsetHeight,
3                      html.clientHeight, html.scrollHeight, html.offsetHeight );
4