Here, `this._elements` would be passed into callee from the caller.

And because we have to find out the elements ('input[type=checkbox]:checked') at runtime when calling this method, we have to query these sub-elements at this timing. 

Or you want to to pass elements like this `_deleteCertificate(checkedInputList, subElements)` ? But this way, we would make our code hard to understand and increase the effort.