How can i convert the purpose of this code from getting sourse of current page to my website using chrome extension

Question

Hi I'm working on chrome extension app for my website. The problem is I found some code that will give me what I want - the purpose for this code is to give me the source code of the current page, but I want to take source code for link

I want to define it inside the code

I didn't understand from where they get the current page to change it to the link which I want to get the source of.

This is the stack code which I found

https://stackoverflow.com/a/11696154/3587326

now what i want is any one who can convert this code from current page to page i need to define it inside the code popup.js

chrome.extension.onMessage.addListener(function(request, sender) {
  if (request.action == "getSource") {
    message.innerText = request.source;
  }
});

function onWindowLoad() {

  var message = document.querySelector('#message');

  chrome.tabs.executeScript(null, {
    file: "getPagesSource.js"
  }, function() {
    // If you try and inject into an extensions page or the webstore/NTP you'll get an error
    if (chrome.extension.lastError) {
      message.innerText = 'There was an error injecting script : \n' + chrome.extension.lastError.message;
    }
  });

}

window.onload = onWindowLoad;

getPagesSource.js

function DOMtoString(document_root) {
    var html = '',
        node = document_root.firstChild;
    while (node) {
        switch (node.nodeType) {
        case Node.ELEMENT_NODE:
            html += node.outerHTML;
            break;
        case Node.TEXT_NODE:
            html += node.nodeValue;
            break;
        case Node.CDATA_SECTION_NODE:
            html += '<![CDATA[' + node.nodeValue + ']]>';
            break;
        case Node.COMMENT_NODE:
            html += '<!--' + node.nodeValue + '-->';
            break;
        case Node.DOCUMENT_TYPE_NODE:
            // (X)HTML documents are identified by public identifiers
            html += "<!DOCTYPE " + node.name + (node.publicId ? ' PUBLIC "' + node.publicId + '"' : '') + (!node.publicId && node.systemId ? ' SYSTEM' : '') + (node.systemId ? ' "' + node.systemId + '"' : '') + '>\n';
            break;
        }
        node = node.nextSibling;
    }
    return html;
}

chrome.extension.sendMessage({
    action: "getSource",
    source: DOMtoString(document)
});