javascript - Is there a way to check document.ready() if jQuery is not available?

I know you can use the window.onload event to make functions run, but is there a way for a script to query if the document is ready or not?

Something like

function update()
{
    if( !document.ready() )  // don't do unless document loaded
        return ;
}
window.setInterval( 'update();', 100 ) ;

Cannot change the element, and no jQuery/other libraries.

Answer

Here you go:

var tid = setInterval( function () {
    if ( document.readyState !== 'complete' ) return;
    clearInterval( tid );       
    // do your work
}, 100 );

Read about the document.readyState property here. I am not sure if all current browsers implement it.