CSS hover in Javascript

Question

I create an element like: var btn = document.createElement("BUTTON");

Then I append it to the DOM like: document.getElementsByClassName("text")[0].appendChild(btn);

I want to change the onHover property for the button. I want to achieve something like:

btn.style.onHover ="background: #3cb0fd";

OR

btn.style.backgroundColor.onHover ="#3cb0fd";

I am not sure what's the right code for this.