addEvenListener doesn't work on dynamic button - javascript

问题:

So I'm currently busy with learning JavaScript. I created some dynamic buttons and I tried to add an addEvenListener to it. But it doesn't work and I can't figure it out why it doesn't work. I'm just testing some stuff and I try to create buttons with values from the localstorage. It is almost working, only the addEvenListener isn't working. I just want a simple alert with the key from the localstorage.

for (var i = 0; i <= localStorage.length-1; i++) {     var categoryButton = document.createElement('input');     categoryButton.setAttribute('class', 'forumMenu');     categoryButton.setAttribute('type', 'button');     categoryButton.setAttribute('name', localStorage.key(i));     categoryButton.setAttribute('value', localStorage.key(i));     categoryButton.setAttribute('id', localStorage.key(i));     categoryButton.addEventListener('click', function(col){     alert(col); }(localStorage.key(i)),true);     forumMenu.appendChild(categoryButton); } 

Does anyone know why it doesn't work?

回答1:

You're not passing a function to EventTarget.addEventListener(). You're immediately executing and passing the result of this:

function (col) {   console.log(col); }(localStorage.key(i)) 

... which is undefined. You can ammend that by using the following syntax:

categoryButton.addEventListener('click', (function(col) {     // return a function to addEventListener    return function(){       console.log(col);    } })(localStorage.key(i)),true); 

Here's a demo:

var input; for (var i = 0; i <= 5; i++) {   input = document.createElement('input');   input.type = "button"   input.value = i;   input.addEventListener('click', function(i) {     // return a function to addEventListener     return function() {       console.log(i);     }   }(i), true);   document.body.appendChild(input); }

回答2:

You stored the value in the id attribute, so just use it:

 for (var i = 0; i <= localStorage.length-1; i++) {     var categoryButton = document.createElement('input');     categoryButton.setAttribute('class', 'forumMenu');     categoryButton.setAttribute('type', 'button');     categoryButton.setAttribute('name', localStorage.key(i));     categoryButton.setAttribute('value', localStorage.key(i));     categoryButton.setAttribute('id', localStorage.key(i));      categoryButton.addEventListener('click', function () {alert(this.getAttribute('id'));});  document.body.appendChild(categoryButton);  } 

In the event handler, this references the <input> element itself, so you can just retrieve the attribute value.

回答3:

Thats because you are assigning that eventlistener to an object that is not still in the DOM (thats because you created this element after the DOM was loaded)

Try this:

categoryButton.onclick = function(col){     alert(col); } 

You can either declare a function to a var and then reasign this function to the event handler:

var myFunction = function(){     alert("I'm a function"); }  myElement.onclick = myFunction; 

文章来源: addEvenListener doesn't work on dynamic button - javascript