Accessing the DOM returns null in lightning component

Question

Somewhat new to Salesforce. I have a lightning component that has an iframe in it. The component will be in the lightning communities. There is a method in the controller that gets called once the iframe is loaded. For some reason I can't access any DOM elements, it's always null. Here's an example snippet:

Component

<aura:component implements="forceCommunity:availableForAllPageTypes">
     <iframe src="/mypage" onload="{!c.iframeOnLoad}" class="myIframe" frameBorder="0"/>
</aura:component>

Controller

({       
    iframeOnLoad: function(){
        try{
           customCss = document.getElementById('customCSS').innerHTML;
        }
        catch(ex){
           console.log(ex);
        }
    }
})

The customCss element is actually there but for some reason it's not getting it. If I put that js snippet in the browser console, it does get the innerHTML in that element. I hope that understands it.

Answer 1

DOM manipulation, due to this critical update "Enable Lightning LockerService Security", will be not more usable. Instead, you can use component.set and component.get lightning pure methods.