Iframe.readyState does not work in chrome

Please try this - you are really mixing dom and jQuery from line to line

var tId;

function stopAnim() {
    // I stop the animation and show the page
    animation.hide();
    progressBar.hide();
    $('#page').show();
    clearInterval(tId);
}
var iframe = $("<iframe />");
iframe.css("visibility","hidden");

iframe.on("readystatechange",function() {
 if (this.readyState == "complete" || this.readyState == "interactive") {
   stopAnim();
 }
});
iframe.on("load",function() { // can possibly be deleted
 if (tId) {
   stopAnim();
 }
});

iframe.attr("src","GetFile.aspx?file=" + fileName);
$("body").append(iframe);
tId = setInterval(function() {
  // update progress here
}, 1000); // 

The downloadable file content doesn't trigger the readystatechange event handler or the onload event handler. This couse you can set a cookie in server side together the file content, and client side check this cookie periodically. For example:

server

response.cookie('fileDownloaded','true');
response.header('attachment','your-file-name.any');
//...write bytes to response...

client

var checker = setInterval(()=>{
    if(document.cookie.indexOf('fileDownloaded')>-1){
        alert('done');
        clearInterval(checker);
    }
},100);

Of course, you can use your framework to check the cookie value correctly, this is just a poc, not a safe cookie parser.

You can use the onload to signaling the load of the iframe

here is a simple example that working

var iframe = document.createElement("iframe");
iframe.style.display = "none";
// this function will called when the iframe loaded
iframe.onload = function (){
  iframe.style.display = "block";    
  alert("loaded");
};
// set the src last.
iframe.src ='http://www.test.com';

// add it to the page.
document.getElementById("one").appendChild(iframe);

Tested here:
http://jsfiddle.net/48MQW/5/
With src loaded last.
http://jsfiddle.net/48MQW/24/