getElById: ElementRef = function(id) {
  return document.getElementById(id);
}
// ES 6:
getElById = id: string => document.getElementById();

getVisiblility = elem: ElementRef => elem.style.visibility;
getDisplayProp = elem: ElementRef => elem.style.display;

var visibility = getVisibility(getElById('someId'));

isHidden = id: string => getVisibility(getElById('someId')) === 'hidden';
isNotDisplayed = id: string => getDisplayProp(getElById('someId')) === 'none';

if(isHidden(getElById(id))) {
  doSth()
}