watir-webdriver - clicking Javascript button

First week with watir-webdriver and Web app testing in general, so still trying to wrap some concepts around.

Having this javascript element:

<input type="submit" class="button" value="Search" name="_target0">

browser.button(:value, "Search").exists?
=> "true"

browser.button(:value, "Pesquisar").present?
=> true

browser.button(:name, "_target0").value
=> "Search"

This doesn't actually drive the button to get clicked,

browser.button(:name, "_target0").click

So I got the driven Firefox clicking the button using either

browser.button(:name, "_target0").fire_event('on_click')
browser.button(:name, "_target0").when_present.click

but what are the differences between them?

Solution

As far as the differences between them:

.click = simulates a left mouse click on the object.
.fire_event = executes a javascript even that may or may not be accessible normally via mouse click.
when_present.click = waits for the object to be both available and appear in the viewable area (full browser window) before it attempts to click.

when_present is useful for when your site uses AJAX, and interacting with one object causes another object to eventually appear. Using a .click may attempt to click the second object before it is available, and the script will fail.

It is likely that your page contains an AJAX form, and the button you are attempting to interact with does not load immediately, but after a short delay when:

a text field is entered
another button is clicked
the page finishes generating content
etc.

Since fire_event does not look for the physical representation of the button, but rather the JS event in the source, it can be used before the button is present/visible/actionable.