calcvh.js

function canCalcVh() {
  //If we don't have this, calc + vh probably won't work anyway.
  if (!window.getComputedStyle) return false;

  //Create a div element
  var dummyDiv = document.createElement('div');
  
  //Ensure it's not visible
  dummyDiv.style.visibility = 'hidden';
  
  //Set a calc style on it
  dummyDiv.style.height = 'calc(1px + 50vh)'
  
  //Add it to the dom so it gets a style
  document.body.appendChild(dummyDiv);
  
  //Get it's actual computed height
  var renderedHeight = parseInt(window.getComputedStyle(dummyDiv).height, 10);
  
  //If it's > 0, then calc with vh must be working
  return renderedHeight > 0;
}