robot-hands-without-jquery.js

// Old-school ES5 way
function toggle () {
  for (var i = 0; i < element.length; i++) {
    if (element[i].style.opacity === '0') {
      element[i].style.opacity = '1';
    } else {
      element[i].style.opacity = '0';
    }
  }
}

// Modern ES6 methods
// Include polyfill.io to ensure backwards compatibility
var elements = document.querySelectorAll('.robot');
setInterval(toggle, 800);

function toggle () {
  Array.from(elements).forEach(function (element) {
    if (element.style.opacity === '0') {
      element.style.opacity = '1';
    } else {
      element.style.opacity = '0';
    }
  });
}