You can do so by adding an event listener to the document object for the DOMContentLoaded event:

document.addEventListener('DOMContentLoaded', (event) => {
  //the event occurred
})

I usually don’t use arrow functions inside for the event callback, because we cannot access this.

In this case we don’t need so, because this is always document. In any other event listener I would just use a regular function:

document.addEventListener('DOMContentLoaded', function(event) {
  //the event occurred
})

for example if I’m adding the event listener inside a loop and I don’t really know what this will be when the event is triggered.