To get the text content
document.getElementById ( "tdid" ).innerText
or
document.getElementById ( "tdid" ).textContent
var tdElem = document.getElementById ( "tdid" );
var tdText = tdElem.innerText | tdElem.textContent;
If you can use jQuery then you can use
$("#tdid").text();
To get the HTML content
var tdElem = document.getElementById ( "tdid" );
var tdText = tdElem.innerHTML;
in jQuery
$("#tdid").html();