iframe example - use an onLoad callback instead of the ref

[adrid]

Description
Makes the iframe example work on the Firefox and keeps it working on other browsers. It changes using the ref on the iframe to an onLoad event solution

Issue
Fixes: #4285

Example
https://www.slatejs.org/examples/iframe on the Firefox

Context
Firefox resets the iframe content on the load event. I've tested on some older versions of the browser and it keeps happening too. Here is an issue on the react repo facebook/react#22847

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)

[changeset-bot]

⚠️ No Changeset found

Latest commit: d1602fc

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[nemanja-tosic]

Just to make sure, it would not be possible to pass in onLoad load anymore. Is that intentional?

[adrid]

Just to make sure, it would not be possible to pass in onLoad load anymore. Is that intentional?

Yes. I don't think this is needed for this example.

[dylans]

@adrid, this change has broken our integration test. Any chance you have time to update the test to reflect the change in the example?

  iframe editor
    1) should be editable


  0 passing (10s)
  1 failing

  1) iframe editor
       should be editable:
     TestingLibraryElementError: Timed out retrying after 4000ms: Unable to find an accessible element with the role "textbox"

There are no accessible roles. But there might be some inaccessible roles. If you wish to access them, then set the `hidden` option to `true`. Learn more about this here: https://testing-library.com/docs/dom-testing-library/api-queries#byrole
      at Object.getElementError (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:1764:17)
      at eval (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:2729:25)
      at eval (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:2701:24)
      at eval (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:2754:25)
      at baseCommandImpl (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:477:16)
      at commandImpl (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:480:40)
      at getValue (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:504:23)
      at resolveValue (http://localhost:3000/__cypress/tests?p=cypress/support/index.ts:544:35)




  (Results)

  ┌────────────────────────────────────────────────────────────────────────────────────────────────┐
  │ Tests:        1                                                                                │
  │ Passing:      0                                                                                │
  │ Failing:      1                                                                                │
  │ Pending:      0                                                                                │
  │ Skipped:      0                                                                                │
  │ Screenshots:  1                                                                                │
  │ Video:        true                                                                             │
  │ Duration:     10 seconds                                                                       │
  │ Spec Ran:     examples/iframe.ts                                                               │
  └────────────────────────────────────────────────────────────────────────────────────────────────┘

[adrid]

@dylans when I created the pull request it was not passing this test and I noticed that later - the same thing what you pointing out.

I've already fixed it here in the next commit 87a8604

I've tested on the main branch (as all those commits are merged) and seems to be okay so maybe you referring to some check before I fixed that?