jQuery event.isDefaultPrevented()

What You’ll Learn

event.isDefaultPrevented() returns whether event.preventDefault() was called on this event. This tutorial covers the official link demo, blocking navigation and form submit, coordinating multiple handlers, return false, and comparing with native defaultPrevented.

Introduction

Many events have a default browser action — links navigate, forms submit, checkboxes toggle. Calling event.preventDefault() cancels that action. But how does a later handler know cancellation already happened? Call event.isDefaultPrevented().

jQuery has exposed this check since version 1.3 on its normalized event object. The official demo alerts false, calls preventDefault(), then alerts true — proving the flag flips when default action is blocked.

Understanding event.isDefaultPrevented()

This method answers one question: was default action cancelled on this event?

• Before preventDefault — event.isDefaultPrevented() returns false.
• After preventDefault — returns true for the rest of that event dispatch.
• Read-only — takes no arguments; does not change state.
• Multiple handlers — a later handler can branch on the flag set by an earlier one.

📝 Syntax

Official jQuery API form (since 1.3):

event.isDefaultPrevented()

// typical pattern:
$( "a" ).on( "click", function ( event ) {
  if ( !event.isDefaultPrevented() ) {
    // default not cancelled yet
  }
  event.preventDefault();
  if ( event.isDefaultPrevented() ) {
    // now true
  }
});

Parameters

• None — this method does not accept any arguments.

Return value

• Boolean — true if event.preventDefault() was called on this event object; otherwise false.

Official jQuery API example

$( "a" ).on( "click", function ( event ) {
  alert( event.isDefaultPrevented() ); // false
  event.preventDefault();
  alert( event.isDefaultPrevented() ); // true
});

Examples Gallery

Example 1 follows the official jQuery demo. Examples 2–5 cover links, form submit, chained handlers, and return false.

$( "a" ).on( "click", function ( event ) {
  alert( event.isDefaultPrevented() ); // false
  event.preventDefault();
  alert( event.isDefaultPrevented() ); // true
});

First alert: false
Second alert: true (after preventDefault)
Link does not navigate

$( "#spa-link" ).on( "click", function ( event ) {
  event.preventDefault();
  $( "#status" ).text(
    "Default prevented: " + event.isDefaultPrevented()
  );
});

#status shows "Default prevented: true"
Page stays on same URL — no navigation

$( "#myForm" ).on( "submit", function ( event ) {
  event.preventDefault();
});

$( "#myForm" ).on( "submit", function ( event ) {
  console.log( "Submit default prevented?", event.isDefaultPrevented() );
});

Submit default prevented? true
Form does not reload the page

$( document ).on( "click", "a.external", function ( event ) {
  if ( event.isDefaultPrevented() ) return;
  event.preventDefault();
  window.open( this.href, "_blank" );
});

If another handler already called preventDefault → this handler returns early
Otherwise → opens link in new tab via window.open

$( "#btn" ).on( "click", function ( event ) {
  console.log( "before:", event.isDefaultPrevented() );
  return false;
});

$( "#btn" ).on( "click", function ( event ) {
  console.log( "after sibling:", event.isDefaultPrevented() );
});

before: false
(after first handler return false — propagation may stop; pattern shows preventDefault effect when handlers both run on same element order permitting)

🚀 Common Use Cases

• Debug handlers — log isDefaultPrevented() after custom logic runs.
• AJAX forms — confirm submit was prevented before sending XHR.
• Link interceptors — skip fallback when another plugin already prevented navigation.
• Validation plugins — invalid field handlers call preventDefault(); analytics handlers check the flag.
• Testing — assert isDefaultPrevented() after simulating clicks in Try-it labs.
• Library cooperation — avoid double preventDefault when integrating third-party code.

📝 Notes

• Available since jQuery 1.3 — returns a Boolean.
• Takes no arguments — read-only query method.
• Reports whether preventDefault() was ever called on this event object.
• Does not report propagation state — use isPropagationStopped() for that.
• return false in jQuery handlers also sets default prevented.
• Native defaultPrevented property exists on modern events; jQuery wraps consistently.

💡 Best Practices