Equal heights in pure JS
The two loops are necessary:
to know the max value, you need to make one complete pass.
There's no way around it.
Only after you know the max value,
after checking all items,
you need a second pass to set the height to the max.

In terms of writing style,
there isn't really a standard,
and it may be a matter of taste,
but in any case I prefer this way:

var maxHeight = -1;
var elems = document.getElementsByClassName("features");

for (var i = 0; i &lt; elems.length; i++) {
    maxHeight = maxHeight &gt; elems[i].offsetHeight ? maxHeight : elems[i].offsetHeight;
}

for (var i = 0; i &lt; elems.length; i++) {
    elems[i].style.height = maxHeight + "px";
}