Difference between Javascript setTimeout() and WebConfig sessionState timeout

In Javascript, setTimeout("asd()",1000) it timeout after 1000 seconds while timeout in sessionState of webconfig uses minutes.

Does these two have the same function as in when it goes into a new page, no matter how long it takes to generate the page, it will start counting whenever it goes into the page?

In javascript, i put it under an in the html page. So does it start counting timeout when the label is loaded?

Then what about the setting in the webconfig, how it starts counting timeout?