Detect if a key should be treated as a style or attribute

I have the following function :

var applyStyling = function (element, object) {
    return _.each(object, function (value, key) {
       // determine whether the key should be treated as an attribute or style 
         if(style)
            element.style.key = value
         element.setAttribute(key, value)
    })
}

An example use would be something like

applyStyling('some dom element', {'id' : 'someID', 'zIndex' : 10})

How can I detect if the key should be treated as a style or attribute? I could only find how to check if attribute/style has been set on an element.