I'm writing a simple userscript that will auto-hide a Facebook post if it contains a certain list of words. The core functionality works, but my MutationObserver
doesn't seem to read the className
of mutation.addedNodes
properly. I loop through mutation.addedNodes
and check if any of those elements have the class userContentWrapper
, but the result of that test is always false -- even if the element does have the class.
var startObserver = function() {
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
var added = mutation.addedNodes;
for (var i = 0; i < added.length; i++) {
if (/\buserContentWrapper\b/.test(added[i].className)) {
processFilter(added[i]);
}
}
});
});
var obj = {childList: true, subtree: true, attributes: true};
observer.observe(document.documentElement, obj);
};
I can only assume that the observer is analyzing the added node before it's fully formed with all the attributes in place. How can I make the observer wait to process the node until it's fully complete? Or am I not understanding the problem?
Thanks in advance...
Some of the added nodes are containers so you should check their insides:
const observer = new MutationObserver(onMutation);
observer.observe(document, {
childList: true,
subtree: true,
});
function onMutation(mutations) {
const found = [];
for (const { addedNodes } of mutations) {
for (const node of addedNodes) {
if (!node.tagName) continue; // not an element
if (node.classList.contains('userContentWrapper')) {
found.push(node);
} else if (node.firstElementChild) {
found.push(...node.getElementsByClassName('userContentWrapper'));
}
}
}
found.forEach(processFilter);
}
MutationObserver callback is executed as a microtask that blocks DOM and JS engine so try to make it fast, especially if it runs on a complex site such as facebook that generates lots of DOM mutations. This can be tested in devtools (F12 key) profiler/timeline panels.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With