How can I make sure that a web-page opens up with scrollbar in the middle

Question

I am trying to create a horizontally scrolling page and I want the page to open with scroll bar in the middle so that the user has option to scroll in both left and right directions(by default it opens with scrollbar at left). How can I do that?

Answer 1

Updated after comment If the body's width doesn't exceed the browser's viewport:
Scrolling inside an element:

var elem = document.getElementById("container"); //div#container
var elemWidth = elem.scrollWidth;
var elemVisibleWidth = elem.offsetWidth;
elem.scrollLeft = (elemWidth - elemVisibleWidth) / 2;

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Use this code to vertically & horizontally center a page (see also: this answer):

 window.scrollTo(
     (document.body.offsetWidth -window.innerWidth )/2,
     (document.body.offsetHeight-window.innerHeight)/2
 );

To only center horizontally, use:

window.scrollTo((document.body.offsetWidth -window.innerWidth )/2, 0);