Good to cache this and others locally so you are not doing an object reference twice. For instance:
```js
var fillColor = style.fillcolor;
if (typeof fillColor !== 'undefined') {
   symbolStyle += 'background-color: ' + fillColor + ';';
}
```
That way you are retrieving the property only once versus twice if the property is defined. Same should be done for the other instances in this code block.