How to subscribe the load event of iframe?

[Fnxxxxo]

What Is the issue?

Are there any way to get the irame element after init of postmate? I need to check if the content document is ready. In case of 404 and 500, I can not relay on the customized load event from the child.

Provide issue context below using code examples, images, or links

Maybe add a load event callback when init postmate?

new Postmate({
  onload: () => {}
})

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[EmanuelAguilar74]

new Postmate() returns a promise, you can use ".then( child => child)" or ".catch()" for the errors I suppose.
The child object has an iframe property inside.