How to detect whether an iframe is loaded with JavaScript?

To detect whether an iframe is loaded with JavaScript, we set the onload property of the iframe to a function that’s called when the iframe is loaded.

For instance, we write

<iframe style="display: none" id="MainPopupIframe" src=""></iframe>

to add the iframe.

Then we write

const ifr = document.getElementById("MainPopupIframe");
ifr.onload = () => {
  console.log("loaded the iframe");
};

to select the iframe with getElementById.

And then we set its onload property to a function that’s called when the iframe is loaded.