Which handlers run?
الأهمية: 5
There’s a button in the variable. There are no handlers on it.
Which handlers run on click after the following code? Which alerts show up?
button.addEventListener("click", () => alert("1"));
button.removeEventListener("click", () => alert("1"));
button.onclick = () => alert(2);The answer: 1 and 2.
The first handler triggers, because it’s not removed by removeEventListener. To remove the handler we need to pass exactly the function that was assigned. And in the code a new function is passed, that looks the same, but is still another function.
To remove a function object, we need to store a reference to it, like this:
function handler() {
alert(1);
}
button.addEventListener("click", handler);
button.removeEventListener("click", handler);The handler button.onclick works independently and in addition to addEventListener.