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Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →To create a custom event in jQuery, attach a handler with .on(), then dispatch that event with .trigger(). You can pass dispatch-time data to the handler, let the event bubble to ancestors, or use .triggerHandler() when you want a narrower, non-bubbling call on only the first matched element.
How to create and trigger a custom event
A custom event is a named signal your code can use to tell other parts of an application that something happened. jQuery does not require a separate event declaration: register a handler for the event name, then trigger it on the element whose listeners should receive it.
- Select the element: create a jQuery collection for the element that will emit the event.
- Register a handler: call
.on("item:added", handler)on that collection. - Dispatch the event: call
.trigger("item:added")on the relevant collection.
For example, a panel can announce that an item was added and include the item as data:
const $panel = $("#panel");
$panel.on("item:added", function (event, item) {
console.log("Added:", item);
});
$panel.trigger("item:added", [{ id: 42, name: "Example" }]);The handler receives the jQuery event object first, followed by any extra arguments supplied when triggering. In this example, item is the object passed in the one-member array. See the jQuery API documentation for .on() and .trigger().
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How to pass data to a handler
Use the second argument to .trigger() for information that becomes available when the event is dispatched. When that argument is an array, each array member becomes a separate handler argument after the event object:
$panel.on("item:added", function (event, item, source) {
console.log(item.name, source);
});
$panel.trigger("item:added", [
{ id: 42, name: "Example" },
"cart"
]);Here, the handler arguments are event, item, and source. A single string or numeric extra argument can be passed without an array wrapper in jQuery 1.6.2 and later. For compatibility with older versions or when supplying multiple values, use an array.
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Do not confuse this with the optional event data supplied to .on(). That data is attached when the handler is registered; extra parameters to .trigger() are provided at dispatch time. The .on() documentation describes event data, while the .trigger() documentation covers extra parameters.
What happens when a custom event is triggered?
.trigger() runs handlers for every element in the jQuery collection. Triggered events bubble up the DOM tree by default, so an ancestor with a matching handler can also observe the event. A handler can stop propagation when the event should not continue upward.
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The event is synthetic: jQuery creates an event object and invokes applicable handlers, but the result is not identical to a naturally occurring event caused by a user’s physical interaction. The jQuery API documentation cautions that .trigger() does not perfectly replicate a naturally-occurring event. Use it to coordinate application code, not as proof that a user actually clicked, typed, or interacted with the browser.
.trigger() vs. .triggerHandler()
Choose based on how broadly the event should run and what result you need:
| Behavior | .trigger() |
.triggerHandler() |
|---|---|---|
| Matched elements | Runs handlers for all elements in the collection. | Runs handlers only on the first matched element. |
| Bubbling | Bubbles through the DOM by default. | Does not bubble. |
| Default action | May cause the associated default behavior. | Does not cause the default action. |
| Return value | Returns the jQuery collection. | Returns the last handler’s return value. |
Use .triggerHandler() when you specifically need jQuery handlers on just the first element, without bubbling or a default action, and want the last handler’s return value. Consult the official .triggerHandler() documentation for details.
Use namespaces to manage custom handlers
A namespace can label a handler so related listeners can be removed selectively. For example, item:added.widget identifies the event name item:added and the namespace widget:
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$panel.on("item:added.widget", handleWidgetItemAdded);
// Remove handlers associated with the widget namespace
$panel.off(".widget");Namespaces are handler-management labels, not hierarchical event types. They are useful when a component needs to clean up its own handlers without removing unrelated listeners. The .on() API documentation explains event names and namespaces.
When not to use .trigger()
If the goal is simply to run a particular function, call that function directly rather than using an event as an indirect function call. A shared function can be called by both the UI handler and other application code, while custom events are better suited to announcing that something happened to any interested listeners. The jQuery Learning Center recommends against using .trigger() simply to execute specific functions. For a broader introduction, see Introducing Custom Events.
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