event.isDefaultPrevented()?event.isDefaultPrevented() returns a Boolean: true if event.preventDefault() was called on this event, otherwise false. Added in jQuery 1.3. Takes no arguments.
event.isDefaultPrevented() // Boolean — no arguments
// Official idea
$("a").on("click", function (event) {
event.isDefaultPrevented(); // false
event.preventDefault();
event.isDefaultPrevented(); // true
});
// Pair with: preventDefault() to cancel
// Not the same as: isPropagationStopped() (bubbling flag)| Need | Use |
|---|---|
| Cancel default | event.preventDefault() |
| Check if cancelled | event.isDefaultPrevented() |
| Stop bubbling | event.stopPropagation() |
| Check bubbling stop | event.isPropagationStopped() |
| Bind handler | .on("click", fn) |
isDefaultPrevented()Call it on the event object before or after preventDefault().
.on() and accept event.event.isDefaultPrevented() early (usually false).event.preventDefault() when you need to cancel the default.event.isDefaultPrevented() again — now true.| Piece | Required? | Role |
|---|---|---|
event | Yes | jQuery event object in the handler |
preventDefault() | To cancel | Sets the flag this method reads |
isDefaultPrevented() | — | Returns true / false |
| Arguments | None | Method takes no parameters |
element.on("click", handler)
when event fires:
flag = false
call handler(event):
event.isDefaultPrevented() → flag // usually false first
if need to cancel:
event.preventDefault()
flag = true
event.isDefaultPrevented() → flag // true after prevent
// Later handler on same event:
if event.isDefaultPrevented():
skip fallback default logic
else:
maybe allow or prevent yourselfKeep these facts handy while coordinating handlers.
| Topic | Detail |
|---|---|
| Returns | Boolean |
| Since | jQuery 1.3 |
| Arguments | None |
| Official demo | false → preventDefault() → true |
return false | Also makes this return true (jQuery) |
| Native cousin | event.defaultPrevented (property) |
| Undo? | No — flag stays set for that event |
| Official docs | api.jquery.com/event.isDefaultPrevented |
Click the link. See the flag before and after preventDefault() — same idea as the official jQuery API demo.
Short, copy-ready snippets. Open DevTools, or use Try It Yourself for a live editor.
Check the flag before and after preventDefault() on a link.
$("a").on("click", function (event) {
var before = event.isDefaultPrevented();
event.preventDefault();
var after = event.isDefaultPrevented();
$("#out").text(
"Before: " + before + "\\nAfter: " + after
);
});false.preventDefault() blocks navigation.true.First handler may prevent; second handler reacts to that state.
$("#go").on("click", function (event) {
if ($("#block").prop("checked")) {
event.preventDefault();
}
});
$("#go").on("click", function (event) {
if (event.isDefaultPrevented()) {
$("#out").text("Blocked — default already prevented.");
} else {
$("#out").text("Allowed — default not prevented.");
}
});preventDefault().isDefaultPrevented() reflects the earlier call.Prevent submit when empty; confirm the flag in the same handler.
$("#form").on("submit", function (event) {
if ($("#name").val().trim() === "") {
event.preventDefault();
}
$("#out").text(
"isDefaultPrevented: " + event.isDefaultPrevented()
);
});preventDefault().false (form may navigate).return false Sets the FlagIn jQuery, return false implies preventDefault() — a second handler sees true.
$("#link").on("click", function () {
return false; // preventDefault + stopPropagation
});
$("#link").on("click", function (event) {
$("#out").text(
"Second handler: isDefaultPrevented = " +
event.isDefaultPrevented()
);
});return false cancels the default (and stops bubbling).isDefaultPrevented() === true.preventDefault() explicitly.Prevent default without stopping bubble — compare the two checks.
$("#child").on("click", function (event) {
event.preventDefault();
$("#out").text(
"defaultPrevented: " + event.isDefaultPrevented() + "\\n" +
"propagationStopped: " + event.isPropagationStopped()
);
});isDefaultPrevented() → true.false — bubbling was not stopped.Watch for these when using isDefaultPrevented().
Once preventDefault() runs, the default stays cancelled for that dispatch.
A later handler only sees true if an earlier one (or itself) already called preventDefault().
return false also sets itIn jQuery, return false implies prevent + stop bubble. Prefer explicit preventDefault().
Use isPropagationStopped() for stopPropagation() state.
event.isDefaultPrevented() is a jQuery event-object method available since 1.3. It mirrors the idea of the native defaultPrevented property on a normalized event. Works wherever your loaded jQuery version runs.
Supported in jQuery 1.3–3.x. Prefer jQuery 3.x with .on() handlers. Native equivalent: event.defaultPrevented (boolean property).
Bottom line: Safe for production. Call preventDefault() to cancel; call isDefaultPrevented() to ask whether it already happened.
| Approach | Cost | Best for |
|---|---|---|
event.isDefaultPrevented() | Free | Reading a boolean flag |
event.preventDefault() | Cheap | Cancelling navigation / submit |
| Many handlers checking the flag | Cheap | Coordinating plugin + app handlers |
The method is a simple flag read. Use it when coordination matters — not on every single handler by habit.
preventDefault() already ran.false then true after prevent (official demo).isPropagationStopped() for that flag.One line: isDefaultPrevented() answers “did someone already cancel the default?”
Stop remaining handlers on the same element and bubbling.
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