Menu > Submenu

<!-- html -->

<li id="submenuli">
 <i class="dashicons dashicons-welcome-write-blog"></i><span> Editar Paginas</span>
 <ul id="sub-menu" class='hide'>
 <li>Sobre dashing.net</li>
 </ul>
</li>

/ css /
.hide { display: none }

/ javascript /

var $submenu = document.getElementById('sub-menu'),
 $submenuLi = document.getElementById('submenuli');

$submenuLi.onclick = function(){
 $submenu.classList.toggle('hide');
};

DEMO

____

Ou então:

<li id="submenuli">
 <i class="dashicons dashicons-welcome-write-blog"></i><span> Editar Paginas</span>
 <ul id="sub-menu">
 <li>Sobre dashing.net</li>
 </ul>
</li>

var $submenu = document.getElementById('sub-menu'),
 $submenuLi = document.getElementById('submenuli');
 $submenu.style.display = 'none';

$submenuLi.onclick = function(){
 var display = window.getComputedStyle($submenu, null)
 .getPropertyValue('display');
 $submenu.style.display = (display == 'block') ? 'none' : 'block';
}

DEMO