Setting top and left CSS attributes

div.style yields an object (CSSStyleDeclaration). Since it's an object, you can alternatively use the following:

div.style["top"] = "200px";
div.style["left"] = "200px";

This is useful, for example, if you need to access a "variable" property:

div.style[prop] = "200px";

Your problem is that the top and left properties require a unit of measure, not just a bare number:

div.style.top = "200px";
div.style.left = "200px";

You can also use the setProperty method like below

document.getElementById('divName').style.setProperty("top", "100px");