document.getElementById(\'frmMain\').elements
can i use like this
document.getElementByName(\'frmMain\').elements
I assume you are talking about getElementById() returning a reference to an element whilst the others return a node list. Just subscript the nodelist for the others, e.g. document.getElementBytag('table')[4].
Also, elements is only a property of a form (HTMLFormElement), not a table such as in your example.