There are three events that signify the current state of the document:
The onload event fires after the document is loaded and all the elements on the page have been completely downloaded.
The onreadystatechange event fires when the document changes from initializing to interactive, and from interactive to loaded.
A document is interactive as soon as the user can interact with it by scrolling or clicking on anchors or elements.
A document is loaded when all the content has been downloaded and rendered in the user’s browser.
The onunload event fires immediately prior to the document being unloaded, as when navigating to another document.