Can you clarify the typescript type of the Mutation list within the callback function of the mutation observer?

Can you provide the typescript data type of the variable mutationList in the callback function?

const targetNode = document.getElementById("some-id");

const config = { attributes: true, childList: true, subtree: true };

const callback = (mutationList, observer) => {
  for (const mutation of mutationList) {
    if (mutation.type === "childList") {
      console.log("A child node has been added or removed.");
    } else if (mutation.type === "attributes") {
      console.log(`The ${mutation.attributeName} attribute was modified.`);
    }
  }
};

const observer = new MutationObserver(callback);

observer.observe(targetNode, config);

Answer №1

List of Mutation Records

const handleMutations = (mutationsList: MutationRecord[], observer: MutationObserver) => {
  for (const mutation of mutationsList) {
    if (mutation.type === "childList") {
      console.log("A child node has been added or removed.");
    } else if (mutation.type === "attributes") {
      console.log(`The ${mutation.attributeName} attribute was modified.`);
    }
  }
};

or

const handleMutations: MutationCallback = (mutationsList, observer) => {
  for (const mutation of mutationsList) {
    if (mutation.type === "childList") {
      console.log("A child node has been added or removed.");
    } else if (mutation.type === "attributes") {
      console.log(`The ${mutation.attributeName} attribute was modified.`);
    }
  }
};

Tip: Define a specific type for the callback function instead of specifying it for each parameter individually.

interface MutationCallback {
    (mutations: MutationRecord[], observer: MutationObserver): void;
}

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