Onclick Doesn't Work When Dynamically Creating Div

I'm a JavaScript noob, and I'm playing with it. I have some code which created a div inside another div by using the innerHTML of the outer div. That had an onclick event which worked fine. Now I'm trying to create the div as an object, so I'm doing something like this:

Code JavaScript:

var obj = document.createElement('div');
obj.id = "object";
obj.onClick = function() {alert("Clicked");};
obj.innerHTML = "something"; // an img tag in the actual code
document.getElementById('objects').appendChild(obj);

The new div is shown, but clicking on it does nothing. (I originally had another function, but changed to the alert for testing.)