自定义下拉列表不'change'事件

Question

我用W3c示例创建了一个自定义下拉列表https://www.w3schools.com/howto/howto_custom_select.asp

它工作正常，但问题是它不能处理更改事件，请参阅下面的示例，打开控制台面板，当您用实际下拉菜单更改选项时，它将显示"；CHANGE"；但是当您使用自定义下拉列表进行更改时，它不会触发更改事件。

https://codepen.io/danishadeel/pen/XWVddpW

var x, i, j, l, ll, selElmnt, a, b, c;
/* Look for any elements with the class "custom-select": */
x = document.getElementsByClassName("custom-select");
l = x.length;
for (i = 0; i < l; i++) {
selElmnt = x[i].getElementsByTagName("select")[0];
ll = selElmnt.length;
/* For each element, create a new DIV that will act as the selected item: */
a = document.createElement("DIV");
a.setAttribute("class", "select-selected");
a.innerHTML = selElmnt.options[selElmnt.selectedIndex].innerHTML;
x[i].appendChild(a);
/* For each element, create a new DIV that will contain the option list: */
b = document.createElement("DIV");
b.setAttribute("class", "select-items select-hide");
for (j = 1; j < ll; j++) {
/* For each option in the original select element,
create a new DIV that will act as an option item: */
c = document.createElement("DIV");
c.innerHTML = selElmnt.options[j].innerHTML;
c.addEventListener("click", function(e) {
/* When an item is clicked, update the original select box,
and the selected item: */
var y, i, k, s, h, sl, yl;
s = this.parentNode.parentNode.getElementsByTagName("select")[0];
sl = s.length;
h = this.parentNode.previousSibling;
for (i = 0; i < sl; i++) {
if (s.options[i].innerHTML == this.innerHTML) {
s.selectedIndex = i;
h.innerHTML = this.innerHTML;
y = this.parentNode.getElementsByClassName("same-as-selected");
yl = y.length;
for (k = 0; k < yl; k++) {
y[k].removeAttribute("class");
}
this.setAttribute("class", "same-as-selected");
break;
}
}
h.click();
});
b.appendChild(c);
}
x[i].appendChild(b);
a.addEventListener("click", function(e) {
/* When the select box is clicked, close any other select boxes,
and open/close the current select box: */
e.stopPropagation();
closeAllSelect(this);
this.nextSibling.classList.toggle("select-hide");
this.classList.toggle("select-arrow-active");
});
}
function closeAllSelect(elmnt) {
/* A function that will close all select boxes in the document,
except the current select box: */
var x, y, i, xl, yl, arrNo = [];
x = document.getElementsByClassName("select-items");
y = document.getElementsByClassName("select-selected");
xl = x.length;
yl = y.length;
for (i = 0; i < yl; i++) {
if (elmnt == y[i]) {
arrNo.push(i)
} else {
y[i].classList.remove("select-arrow-active");
}
}
for (i = 0; i < xl; i++) {
if (arrNo.indexOf(i)) {
x[i].classList.add("select-hide");
}
}
}
/* If the user clicks anywhere outside the select box,
then close all select boxes: */
document.addEventListener("click", closeAllSelect);
$('.custom-select select').on('change', function(){
console.log('CHANGE')
})

Answer 1

事件只有在用户操作触发时才会自动触发。因为您正在以程序方式更改所选项目，所以不会发出任何事件。

您可以使用手动调度事件

s.dispatchEvent(new Event('change'));

这里有一个关于调度和监听事件的好资源

https://developer.mozilla.org/en-US/docs/Web/Events/Creating_and_triggering_events