I have a text file stored on the server and an object in HTML like this:
The object tag has to make a separate request to the server and then load that content. Meanwhile, your JavaScript has already executed and "misses the bus."
Run your code inside the onload event of the object.
Then use .contentDocument.body.childNodes[0].innerHTML to view the text file.
var object = document.getElementById("data");
object.onload = function() {
var data = object.contentDocument.body.childNodes[0].innerHTML;
// use the data
};