docs(api.md): iframe load event

[yanivefraim]

Fixes #1413

After playing around with frames, I figured out that execution order is:

1. frameattached
2. framenavigated
3. Frame's window.onLoad

This means that the two steps are needed:

1. Wait for Frame to be attached
2. Wait for Frame to be loaded

I added a section in Frame docs: Waiting for a frame to be loaded, explaining this concept with the example from #1361.

I think that we might need a better built-in solution for that, something like: page.waitForFrameAttached(frameName)

WDYT?

[yanivefraim]

Closing in favor of a page.waitForFrameAttached(frameName) PR

[gonzaloserrano]

Hi, tried to use page.waitForFrameAttached(1) but got TypeError: page.waitForFrameAttached is not a function. Any hints?

[yanivefraim]

Hi... there is no such method. I suggested to add such a method, but did not do it, yet (not sure if this is something we want to have)

[sean-hill]

@yanivefraim I'm facing an issue where this would be helpful. I have a retarded page I have to write tests against that has a DOM structure like this:

If I call page.childFrames() I get a list of 5 frames, and if for each of those frames I call frame.name() immediately after the page loads, they all return empty strings. However if I wait for an arbitrary amount of time until all the frames have loaded, I get back the frame names for each child. So it'd be nice to have some function to wait for a frame to be loaded.

const childFrames = await page.childFrames()
await Promise.all(childFrames.map(frame => frame.waitForLoad()))
const childFrameNames = childFrames.map(frame => frame.name)

Just a suggestion.