How can i run querySelectorAll if my third-party software does not allow/read <!DOCTYPE> tag?

Question

I am developing a web page that needs to be integrated to my third-party software and outputs to HTML web page. But my software does not allow nor read DOCTYPEs. How can I rework this code without using DOCTYPEs.

note that my problem is not with the codes, but how to remake the codes for them to
work without the DOCTYPE tag

Any help would be much appreciated. Thanks.

Here is the simple code.

BROWSER: INTERNET EXPLORER 8

JS:

function myFunctionClass(){

var mo = document.querySelectorAll(".displayBlockClass");
var getYr = document.getElementById("date1Year");
var m;
for (m = 0; m < mo.length; m++){

if(getYr.value == "2001" || getYr.value == "2003" || getYr.value == "2005"){
   mo[m].style.display = "";
}
else{
   mo[m].style.display = "none";
    }
}
}

Answer 1

If an old version of IE lacks support to document.querySelectorAll in quirks mode and you cannot have a DOCTYPE at the start of a document, you need to use some polyfill. There seems to be a simple polyfill qsa-polyfill-ie7.js that does the job:

if (!document.querySelectorAll) {
  document.querySelectorAll = function(selector) {
  var doc = document,
      head = doc.documentElement.firstChild,
      styleTag = doc.createElement('STYLE');
   head.appendChild(styleTag);
   doc.__qsaels = [];
   styleTag.styleSheet.cssText = selector + 
      "{x:expression(document.__qsaels.push(this))}";
   window.scrollBy(0, 0);
   return doc.__qsaels;
   }
}

Make this executed before first call to document.querySelectorAll