[Feature] Add isAttached or isExisting to element

Summary

Implement an easy way to check whether an element is attached to the DOM.

test('test', async ({ page }) => {
  const isExisting = await page.locator('body').isExisting() // returns true or false
})

It’s really not convenient to do something like this every time

const els = await page.locator('body').elementHandles()
const isExisting = els.length > 0

Existing functionality

Please don’t suggest waiters (wait for state to be attached/not attached, etc), visibility checks (isVisible, isHidden) or similar. This is completely different requests. Thank you

[purepear]

I was also looking for a simple way to assert element presence

I guess we could do:

await expect(page.locator('.item').first()).toHaveCount(1) // to exist
await expect(page.locator('.item')).toHaveCount(0) // not to exist

but it seems like a very common assertion so maybe having toExist()/toBeInTheDocument()/toBePresent() is worth it:

await expect(page.locator('.item')).toExist()
await expect(page.locator('.item')).not.toExist()

BTW @grybykm locator.waitFor() might be helpful in your case:

await page.locator('.item').waitFor({ state: 'attached' })

[grybykm]

It would be also nice to have an assertion for this. Something like this:

await expect(page.locator('body')).toExist()
await expect(page.locator('body')).not.toBeAttached()