Difference between nodeName and tagName

If an SPAN element's nodeName is requested, you will get "SPAN". The same will happen for SPAN element's tagName. But, if a text node is requested for nodeName, it will return "#text" and it's tagName will be "undefined", since it's not really a node.

Check the above using
document.getElementById("yourElementId").nodeName
document.getElementById("yourElementId").tagName