modernizr/feature-detects/css/vhunit.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

/*!
{
  "name": "CSS vh unit",
  "property": "cssvhunit",
  "caniuse": "viewport-units",
  "tags": ["css"],
  "notes": [{
    "name": "Related Modernizr Issue",
    "href": "https://github.com/Modernizr/Modernizr/issues/572"
  },{
    "name": "Similar JSFiddle",
    "href": "http://jsfiddle.net/FWeinb/etnYC/"
  }]
}
!*/
define(['Modernizr', 'testStyles'], function( Modernizr, testStyles ) {
  testStyles('#modernizr { height: 50vh; }', function( elem, rule ) {
    var height = parseInt(window.innerHeight/2,10);
    var compStyle = parseInt((window.getComputedStyle ?
                              getComputedStyle(elem, null) :
                              elem.currentStyle)['height'],10);
    Modernizr.addTest('cssvhunit', compStyle == height);
  });
});