问当按钮处于启用状态时运行javascript函数

EN

var btnElement = document.getElementById("buttonId");

var observer = new MutationObserver(observerChanges);
observer.observe(btnElement, {
    attributes: true,
    subtree: opt.watchChildren,
    childList: opt.watchChildren,
    characterData: true
});

/// when you're done observing
observer.disconnect();

function observerChanges(mutationRecord, mutationObserver) {
    console.log(mutationRecord);
}

var observer = new MutationObserver(function(mutations) {
  if(mutations.some(function(m) { return m.attributeName == 'disabled' && !m.target.disabled; }))
  {
    alert('Button was enabled');
  }
});

observer.observe(targetButton, { attributes: true, childList: false, characterData: false });

<button id="myButton" disabled="disabled">Click</button>

var myButton = document.getElementById('myButton');
myButton.watch("disabled", function() {
    console.log("myButton changed!");
});

myButton.disabled = false; // "myButton changed" will be logged