I am using the Mutation Observer API to listen to DOM mutations:

// Select the node that will be observed for mutations
const targetNode = document.getElementById('some-id');

// Options for the observer (which mutations to observe)
const config = { attributes: true, childList: true, subtree: true };

// Callback function to execute when mutations are observed
const callback = function(mutationsList, observer) {
    for(const mutation of mutationsList) {
        if (mutation.type === 'childList') {
            console.log('mutation:', mutation);
        }
    }
};

// Create an observer instance linked to the callback function
const observer = new MutationObserver(callback);

// Start observing the target node for configured mutations
observer.observe(targetNode, config);

When receiving a childList mutation, I would like to know the state of the DOM before the mutation. But when the callback is called, it is already after. Is there a way to do that?