Javascript Get Multiple elements with multiple classes

How can i get multiple elements in javascript for example:

<p class="zrowOdd"> odd </p>
<p class="zrowEven"> even </p>
<p class="zrowOdd"> odd </p>
<p class="zrowEven"> even </p>

Is it possible to get all that elements in order in X:

var x = document.getElementByClassName("zrowOdd + zrowEven")// I know this 
dont work but just to be clear what i need