Javascript textContent is not working in IE8 or IE7

Javascript textContent is not working in IE8 or IE7

I need to add 2 cell content of a table and display it. Below JavaScript
command works fine in chrome or IE10. But not working in IE8 or 7.
parseFloat(document.getElementById("total").textContent).toFixed(2);
It results,
NaN
Could you please tell me what is the equivalent command in IE7 or IE8 to
read cell content of a table and convert it to float then add..