javascript错误：预期分配或函数调用，而是看到一个表达式

Question

我只是想知道，希望有人能帮助我解决这个错误，我得到的提示是expected an assignment or function call and instead saw an expression，该脚本可以正常工作，但是将其粘贴到jsfiddle.net时，我在行{{ 1}}关于为什么以及如何解决此问题的任何想法？

isObserving ? window.obs() : window.dis();

(function() {
  var isObserving = false;
  var target = document.getElementsByClassName('message')[0];

  var observer = new MutationObserver(function(mutations) {
    mutations.forEach(function(mutation) {
      console.info("EVENT TRIGGERT");
    });
  });

  var config = {
    attributes: true,
    childList: true,
    characterData: true
  };

  window.dis = function() {
    console.log('observer off')
    observer.disconnect();
    ars.innerHTML = "observer off";
  };

  window.obs = function() {
    console.log('observer on')
    observer.observe(target, config);
    ars.innerHTML = "observer on";
  };

  window.toggleObserve = function() {
    isObserving = !isObserving;
    isObserving ? window.obs() : window.dis();
  };
})();

var ars = document.getElementById("ars");
ars.addEventListener("click", toggleObserve);

// simulate change
refreshIntervalId = setInterval(function() {
  document.getElementsByClassName('message')[0].innerHTML = Math.random().toString(36).substring(2, 15);
}, 1000);