On gists
                reveal.js
                    
                        
                        •
                        
                    
                        JavaScript
                      
                    
                    
                    reveal.js
                        Raw
                        #
                    
                        function reveal() {
        var reveals = document.querySelectorAll(".reveal");
        for (var i = 0; i < reveals.length; i++) {
          var windowHeight = window.innerHeight;
          var elementTop = reveals[i].getBoundingClientRect().top;
          var elementVisible = 150;
          if (elementTop < windowHeight - elementVisible) {
            reveals[i].classList.add("active");
          } else {
            reveals[i].classList.remove("active");
          }
        }
      }
      window.addEventListener("scroll", reveal);