Since the operation is not executed, we need to know when the user started the operation and can use event.isDefaultPrevented() to determine whether this method is triggered by the event handler call. This can be used to trigger function calls. This can also be useful for using dynamic URLs of XHR in jQuery, such as href="index.php?page=contact" instead of contact.php to get a page containing a module. You may also want to check out the MOD rewrite option, which also offers this feature and SEO benefits. jQuery Stop event function. If you are using $(document).bind("keydown keypress", function(event), please note that e.preventDefault() will not work, please try event.preventDefault(). Sometimes you have a hyperlink that needs to be a hyperlink, but you don't want it to process and open the link, but just want to call a JavaScript function. Fortunately, there is a function in jQuery that can stop hyperlink operations.

jQuery preventDefault() function demonstration example

Example 1: Block and capture hyperlink clicks

$("a").click(function(event) {
  event.preventDefault();
  $('<div>
<p>')
    .append('默認(rèn) ' + event.type + ' 已阻止')
    .appendTo('#log');
});
</p>
<p><strong>Example 2: Block form submission button </strong></p>
<pre class="brush:php;toolbar:false">$('#myform').submit(function(event) {
    event.preventDefault();
    var self = this;
    window.setTimeout(function() {
        self.submit();
    }, 2000);
});

Example 3: Delay the hyperlink target after animation effect

$("#ELEMENT_WHICH_AFFECT_THE_SLIDEUP")
.click(function(event){
    event.preventDefault(); // 阻止鏈接重定向
    var time = 1000; // slideup 效果的時間
    var url = $(this).attr("href"); // 選擇用于通過 JavaScript 重定向的 URL

    $("#ELEMENT_TO_SLIDE_UP").slideUp(time); // 效果
    window.setTimeout(function(){document.location.href=url;}, time); // 超時并在效果完成后等待
    return -1;
});

Example 4: Disable the keyboard scroll down button

$(document).keydown(function(event){
    // 向下移動
    if(event.keyCode == '40'){
        event.preventDefault();
        var posY = $('#'+selectedTxtID).css('top');
        posY = parseFloat(posY);
        var newPosY = posY + 1;
        $('#'+selectedTxtID).css('top', newPosY+'px');
    }
});

This function can be used not only for hyperlinks, but also for any element with the default action you wish to block.

jQuery preventDefault() method FAQ (FAQ)

What is the main function of jQuery's preventDefault() method?

The preventDefault() method in jQuery is mainly used to prevent the default operation of events from occurring. For example, if you have a link on your web page and you don't want it to redirect to another page when clicked, you can use the preventDefault() method to block this default action. This method is especially useful when you want to control event operations in your code, providing a higher level of interactivity to your web application.

How is the difference between the preventDefault() method and the stopPropagation() method?

Although both methods are used to control event operations, their purposes are different. The preventDefault() method prevents the event from happening, while the stopPropagation() method prevents the event from bubbled up in the DOM tree, preventing any parent handler from receiving event notifications. In other words, preventDefault() handles the default behavior of elements, while stopPropagation() handles the stream of events in the DOM hierarchy.

Can I use the preventDefault() method with all events?

No, preventDefault() method cannot be used with all events. It only works with events with default actions to block. For example, it can be used with the anchor tagged "click" event to prevent the default action of navigating to the new URL. However, it cannot be used with custom events without default actions.

How to check if the preventDefault() method has been called for the event?

You can use the isDefaultPrevented() method to check if preventDefault() is called on the event. This method returns a boolean value—true if preventDefault() is called, otherwise false.

Can I use the preventDefault() method in Internet Explorer?

Yes, you can use the preventDefault() method in Internet Explorer. However, older versions of Internet Explorer (IE8 and below) do not support this method. For these versions, you can use the returnValue property of the event object to achieve the same effect.

What happens if I call preventDefault() on an uncancelable event?

If you call preventDefault() on an uncancelable event, the method will be invalid. An uncancelable event refers to an event that cannot be blocked by its default operation. You can use the cancelable property of the event object to check whether the event is cancelable.

Can I call preventDefault() multiple times for the same event?

Yes, you can call preventDefault() multiple times for the same event, but it won't have any extra effects. Once the default action of the event is blocked, calling preventDefault() again will not change anything.

Can I use preventDefault() with keyboard events?

Yes, you can use preventDefault() with keyboard events. For example, you can block the default action of the "keydown" event to prevent characters from entering text fields.

How to use preventDefault() in a conditional statement?

You can use preventDefault() in the conditional statement to control when events should be blocked. For example, if some verification checks fail, you can prevent form submission.

Can I use preventDefault() with touch events?

Yes, you can use preventDefault() with touch events. For example, you can block the default action of the "touchstart" event to prevent the recognition of touch gestures.