创建和触发事件本文演示如何创建和分派 DOM 事件。此类事件通常称为**合成事件**，与浏览器本身触发的事件相对。
创建自定义事件可以使用 Event 构造函数创建事件，如下所示
jsconst event = new Event("build");
// Listen for the event.
elem.addEventListener(
"build",
(e) => {
/* … */
},
false,
);
// Dispatch the event.
elem.dispatchEvent(event);
以上代码示例使用了 EventTarget.dispatchEvent() 方法。
此构造函数在大多数现代浏览器中受支持。有关更详细的方法，请参阅下面的 旧式方法。
添加自定义数据 – CustomEvent()要向事件对象添加更多数据，可以使用 CustomEvent 接口，并使用**detail**属性传递自定义数据。例如，可以按如下方式创建事件
jsconst event = new CustomEvent("build", { detail: elem.dataset.time });
然后，您可以在事件侦听器中访问这些附加数据
jsfunction eventHandler(e) {
console.log(`The time is: ${e.detail}`);
}
旧式方法创建事件的较旧方法使用受 Java 启发的 API。以下显示了一个使用 document.createEvent() 的示例
js// Create the event.
const event = document.createEvent("Event");
// Define that the event name is 'build'.
event.initEvent("build", true, true);
// Listen for the event.
elem.addEventListener(
"build",
(e) => {
// e.target matches elem
},
false,
);
// target can be any Element or other EventTarget.
elem.dispatchEvent(event);
事件冒泡通常希望从子元素触发事件，并让祖先元素捕获它；可以选择性地携带数据
html
jsconst form = document.querySelector("form");
const textarea = document.querySelector("textarea");
// Create a new event, allow bubbling, and provide any data you want to pass to the "detail" property
const eventAwesome = new CustomEvent("awesome", {
bubbles: true,
detail: { text: () => textarea.value },
});
// The form element listens for the custom "awesome" event and then consoles the output of the passed text() method
form.addEventListener("awesome", (e) => console.log(e.detail.text()));
// As the user types, the textarea inside the form dispatches/triggers the event to fire, and uses itself as the starting point
textarea.addEventListener("input", (e) => e.target.dispatchEvent(eventAwesome));
动态创建和分派事件元素可以侦听尚未创建的事件
html
jsconst form = document.querySelector("form");
const textarea = document.querySelector("textarea");
form.addEventListener("awesome", (e) => console.log(e.detail.text()));
textarea.addEventListener("input", function () {
// Create and dispatch/trigger an event on the fly
// Note: Optionally, we've also leveraged the "function expression" (instead of the "arrow function expression") so "this" will represent the element
this.dispatchEvent(
new CustomEvent("awesome", {
bubbles: true,
detail: { text: () => textarea.value },
}),
);
});
触发内置事件此示例演示了如何使用 DOM 方法模拟对复选框的点击（即以编程方式生成点击事件）。查看示例。
jsfunction simulateClick() {
const event = new MouseEvent("click", {
view: window,
bubbles: true,
cancelable: true,
});
const cb = document.getElementById("checkbox");
const cancelled = !cb.dispatchEvent(event);
if (cancelled) {
// A handler called preventDefault.
alert("cancelled");
} else {
// None of the handlers called preventDefault.
alert("not cancelled");
}
}
另请参阅
CustomEvent()
document.createEvent()
Event.initEvent()
EventTarget.dispatchEvent()
EventTarget.addEventListener()