javascript getElementsByClassName() always returns none?

问题

hey guys, i wanna create the simplest bookmarklet for my browser.

javascript:document.getElementsByClassName('source').style.visibility='visible';

I have multiple div.source in my body. By default they are set to .source { display:none; } with css.

My console tells me: Uncaught TypeError: Cannot set property 'display' of undefined

When I click the bookmarklet all .source divs should be visible. What am I doing wrong here?

回答1:

You might need to loop through the results, like this:

var divs = document.getElementsByClassName('source');
for(var i=0; i<divs.length; i++) { 
  divs[i].style.display='block'
}

And also as @ionoy mentioned, use display attribute. I hope that helps.

http://jsfiddle.net/erick/rb7bn/1/

回答2:

There is 'visibility' and there is 'display'. They are quite different beasts.

W3Schools:

visibility

display

回答3:

Go for display. It's works fine with many browsers and in many cases.

来源：https://stackoverflow.com/questions/5179798/javascript-getelementsbyclassname-always-returns-none