"If you can't make it work without scripting first, you likely have no business adding scripting to it!"
You'll need to store each post either in a static file (which is a security risk and gets very poor performing very quickly) or a database -- which means learning a technology like mySQL, postGreSQL, MSSQL, SQLite, etc, etc...
THEN if you want scripting, to do what you are asking in terms of posting it so other users on their own computers can see it instead of letting the already working form submit normally, you'd trap it's "onsubmit", cancel it, and use AJAX to send the new value instead; which is to say you use a XMLHttpRequest object to send the data, and I'd probably have it check for other updates while at it.
Basically, JS alone isn't gonna do what you are asking, as you'll need a server side language, database language, and a proper normal form submit working first before you even THINK about getting client side scripting involved.
That is, assuming I understood your last post...