Javascript get h2 tag inside li tag and return it

I want to obtain a h2 tag inside an li tag with javascript, not jquery. Currently this is the html:

<li vriend="Alvin Heijmans" select="">
     <img class="portret" src="img/alvin.png" />
     <div class="addbutton"></div>
     <h2>Alvin Heijmans</h2>
     <p>Utrecht</p>
</li>

Now I want to select the h2 tag inside the li using the following javascript:

var elms = document.getElementsByTagName('li');
var names = elms.getElementsByTagName('h2');

The console is giving the following error:

TypeError: elms.getElementsByTagName is not a function
var names = elms.getElementsByTagName('h2');

So how can this be solved?