JavaScript ES6 implementation of element's append event handling.

once, appended, callback, element, append, handler
npm install dom-once-appended@1.0.0


Element append callback implementation

JavaScript ES6 implementation of element's append event handling.

Since browsers (JavaScript) does not provide any API to handle element's append event, we have to use a hacky-tricky solutions for this. There are two "clean" methods discovered for now of how append event can be implemented. Of course, there is a lot more methods of solution, but these ones are fully modular and does not have side effects. Chose one that fits your needs at best.

The first method (onceAppended) uses CSS animations to detect whether element is appended and is based on animationstart event. The second method uses MutationObserver events to detect element append (onceAppendedSync). The second method has poor performance if there are a lot of elements append to the page, while the first method has a little delay of triggering callback (1 frame, around 25ms).

An Example of Usage

Let say we develop a JavaScript module, which knows nothing about the environment it will be used in. Our module returns an element, which needs to be initialized once appended.

To use the trigger, you need to install npm package dom-once-appended:

npm install --save-dev dom-once-appended

After installing the package, you have a choice of which method to use. The example below demonstrates the usage of onceAppended function, while onceAppendedSync function is available as well with the same parameters.

import { onceAppended } from "dom-once-appended";

function myModule () {
    let sampleElement = document.createElement("div");
    onceAppended(sampleElement, () => { // module initialization
        console.log(`Sample element is appended!`);
    return sampleElement;

// somewhere else in the sources (example)
let element = myModule();
setTimeout(() => document.body.appendChild(element), 200);


If you have found a better methods of handling element's append event, have some improvements on existing methods or want to add any functionality, your contributions are welcome. Start by creating an issue on GitHub describing what you have discovered.