Fetch data from all classes having same name using javascript

Fetch data from all classes having same name using javascript

I am new with javascript and the problem I have is that while building a
chrome extension I need to extract data from a website let's say
"www.abc.com". The data that I need is all present in all divs with the
class="className" (say). How can I get the data from that particular
class.
Thanks in advance.