What's the difference between `visible?` and `present?`?

From the Watir API, I've derived two assertions (which of course might not be correct):

I can use exists? if I simply want to verify that the element is in the HTML. I don't care if it's visible or not.
I can use visible?if I want to be able to see it on the page.

So, when do I use present??

It seems to me that I could answer my own question by saying:

I can use present? if I want to be able to see it on the page, but I don't want it to be in the HTML.

So, if I write something on the screen using a marker pen, would that be present??

(Sorry if I seem to be irreverent.)

So - another way to ask the question in the title - when should I use visible? and when should I use present??

The difference between visible? and present? is when the element does not exist in the HTML.

When the element is not in the HTML (ie exists? is false):

visible? will throw an exception.
present? will return false.

I tend to stick with present? since I only care if a user can see the element. I do not care if it cannot be seen due to it being hidden via style, eg display:none;, or not being in the DOM, eg it got deleted. I would only use visible? if the application actually treats the element not being in the DOM as a different meaning than being in the DOM but not visible.

For example, given the page:

<html>
  <body>
    <div id="1" style="block:display;">This text is displayed</div>
    <div id="2" style="block:none;">This text is not displayed</div>
  </body>
</html>

You can see the difference when looking for a div that is not on the page:

browser.div(:id => '3').visible?
#=> Watir::Exception::UnknownObjectException

browser.div(:id => '3').present?
#=> false

For elements on the page, the two methods will be the same:

browser.div(:id => '1').visible?
#=> true
browser.div(:id => '1').present?
#=> true

browser.div(:id => '2').visible?
#=> false
browser.div(:id => '2').present?
#=> false

A comparison of these two methods along with exists? can be found in the Watirways book.

来源：https://stackoverflow.com/questions/25877525/whats-the-difference-between-visible-and-present

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