What's causing this error in my mutation observer using script?

Question

The original question asked has been answered. In addition, someone outside of Stackoverflow has provided a full solution to what I was trying to achieve with my script, which I have added as an answer to my question. The script itself and a summary of the specific problem it solves is detailed in my own answer.

Original Question:

I'm not a programmer, unfortunately, so my experience is very limited.

My browser overwrites a correct img src with an incorrect src a couple of seconds after it starts.

My script's intended function is a work-around to immediately replace the broken src with the correct src again, at the time my browser overwrites the correct src.

function getElementsBySrc(srcValue) {
  var nodes = [];
  var e = document.getElementsByTagName('img');

  for (var i = 0; i < e.length; i++) {
    if (e[i].hasAttribute('src') && e[i].getAttribute('src') == srcValue) {
      nodes.push(e[i]);
    }
  }

  return nodes;
}

function initMod(){
    if(!document.querySelector("#browser")){
        setTimeout(initMod, 1000);
        return;
    }

var targetNode = document.getElementsByTagName('img');
var config = { attributes: true, childList: false, subtree: false, characterData: false };

var callback = function(mutationsList, observer) {
    for(var mutation of mutationsList) {
        if (mutation.type == 'attributes') {

            console.log('The ' + mutation.attributeName + ' attribute was modified.');

            var n = getElementsBySrc('https://hyperspace.marquiskurt.net/icons/favicon-32x32.png');
            for (var i = 0; i < n.length; i++) {
                n[i].setAttribute('src', 'chrome://favicon/https://hyperspace.marquiskurt.net/app/');
            }

        }
    }
};

var observer = new MutationObserver(callback);

observer.observe(targetNode, config);

}
initMod();

The script is loaded directly as my browser starts. My Chrome Devtools Console gives the error:

Uncaught TypeError: Failed to execute 'observe' on 'MutationObserver': parameter 1 is not of type 'Node'.

Answer 1

as document.getElementsByTagName('img'); returns a list of elements, not a node, you can't use targetNode (because it isn't a node)

Here I'm using document.querySelectorAll instead, same result, but it has a forEach method that I use to create the mutation observers for each IMG

function initMod() {
    if(!document.querySelector("#browser")){
        setTimeout(initMod, 1000);
        return;
    }

    const callback = (mutationsList, observer) => {
        for(let mutation of mutationsList) {
            if (mutation.type == 'attributes') {
                console.log('The ' + mutation.attributeName + ' attribute was modified.');
                const n = getElementsBySrc('https://hyperspace.marquiskurt.net/icons/favicon-32x32.png');
                for (let e of n) {
                    e.setAttribute('src', 'chrome://favicon/https://hyperspace.marquiskurt.net/app/');
                }
            }
        }
    };
    const config = { attributes: true, childList: false, subtree: false, characterData: false };
    document.querySelectorAll('img').forEach(targetNode => {
        const observer = new MutationObserver(callback);
        observer.observe(targetNode, config);
    });
}