How Can I Pause JavaScript Execution Until a Specific DOM Element Appears?

How to Pause Your Code Until an Element Appears?

In web development, it's often necessary to perform actions only when specific elements exist on the page. This poses the question of how to determine the presence of an element, especially in asynchronous environments like JavaScript.

Solution: Leveraging MutationObserver API

The MutationObserver API provides a robust solution for detecting changes in the DOM. By creating an observer instance and assigning it to the desired element or its parent, you can set up a callback that will be triggered when a mutation (addition, removal, or attribute change) occurs within the observed area.

Implementation

The provided code snippet demonstrates how to create a reusable waitForElm function using MutationObserver:

function waitForElm(selector) {
    return new Promise(resolve => {
        if (document.querySelector(selector)) {
            return resolve(document.querySelector(selector));
        }

        const observer = new MutationObserver(mutations => {
            if (document.querySelector(selector)) {
                observer.disconnect();
                resolve(document.querySelector(selector));
            }
        });

        observer.observe(document.body, {
            childList: true,
            subtree: true
        });
    });
}

Usage

To wait for an element with the class 'some-class' to appear, you can use:

waitForElm('.some-class').then((elm) => {
    console.log('Element is ready');
    console.log(elm.textContent);
});

Alternatively, with async/await:

const elm = await waitForElm('.some-class');

This approach offers several advantages, including:

• Non-Blocking: It uses the MutationObserver API, which monitors changes passively without blocking the main thread.
• No Dependency: It relies only on native APIs, avoiding the need for third-party libraries.
• Promise-Based: It returns a promise, enabling you to handle the element's appearance conveniently with .then() or async/await.

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