Can I make a <button> not submit a form?

The default value for the type attribute of button elements is "submit". Set it to type="button" to produce a button that doesn't submit the form.

<button type="button">Submit</button>

In the words of the HTML Standard: "Does nothing."

The button element has a default type of submit.

You can make it do nothing by setting a type of button:

<button type="button">Cancel changes</button>

Just use good old HTML:

<input type="button" value="Submit" />

Wrap it as the subject of a link, if you so desire:

<a href="http://somewhere.com"><input type="button" value="Submit" /></a>

Or if you decide you want javascript to provide some other functionality:

<input type="button" value="Cancel" onclick="javascript: someFunctionThatCouldIncludeRedirect();"/>

Yes, you can make a button not submit a form by adding an attribute of type of value button:

<button type="button"><button>

<form onsubmit="return false;">
   ...
</form>

Honestly, I like the other answers. Easy and no need to get into JS. But I noticed that you were asking about jQuery. So for the sake of completeness, in jQuery if you return false with the .click() handler, it will negate the default action of the widget.

See here for an example (and more goodies, too). Here's the documentation, too.

in a nutshell, with your sample code, do this:

<script type="text/javascript">
    $('button[type!=submit]').click(function(){
        // code to cancel changes
        return false;
    });
</script>

<a href="index.html"><button>Cancel changes</button></a>
<button type="submit">Submit</button>

As an added benefit, with this, you can get rid of the anchor tag and just use the button.

Without setting the type attribute, you could also return false from your OnClick handler, and declare the onclick attribute as onclick="return onBtnClick(event)".

  <form class="form-horizontal" method="post">
        <div class="control-group">

            <input type="text" name="subject_code" id="inputEmail" placeholder="Subject Code">
        </div>
        <div class="control-group">
            <input type="text" class="span8" name="title" id="inputPassword" placeholder="Subject Title" required>
        </div>
        <div class="control-group">
            <input type="text" class="span1" name="unit" id="inputPassword" required>
        </div>
            <div class="control-group">
            <label class="control-label" for="inputPassword">Semester</label>
            <div class="controls">
                <select name="semester">
                    <option></option>
                    <option>1st</option>
                    <option>2nd</option>
                </select>
            </div>
        </div>

        <div class="control-group">
            <label class="control-label" for="inputPassword">Deskripsi</label>
            <div class="controls">
                    <textarea name="description" id="ckeditor_full"></textarea>
 <script>CKEDITOR.replace('ckeditor_full');</script>
            </div>
        </div>



        <div class="control-group">
        <div class="controls">

        <button name="save" type="submit" class="btn btn-info"><i class="icon-save"></i> Simpan</button>
        </div>
        </div>
        </form>

        <?php
        if (isset($_POST['save'])){
        $subject_code = $_POST['subject_code'];
        $title = $_POST['title'];
        $unit = $_POST['unit'];
        $description = $_POST['description'];
        $semester = $_POST['semester'];


        $query = mysql_query("select * from subject where subject_code = '$subject_code' ")or die(mysql_error());
        $count = mysql_num_rows($query);

        if ($count > 0){ ?>
        <script>
        alert('Data Sudah Ada');
        </script>
        <?php
        }else{
        mysql_query("insert into subject (subject_code,subject_title,description,unit,semester) values('$subject_code','$title','$description','$unit','$semester')")or die(mysql_error());


        mysql_query("insert into activity_log (date,username,action) values(NOW(),'$user_username','Add Subject $subject_code')")or die(mysql_error());


        ?>
        <script>
        window.location = "subjects.php";
        </script>
        <?php
        }
        }

        ?>