jQuery change event

change event is fired when an element value changes. All the following elements fire this event
1. input 
2. textarea 
3. select 

select, radio buttons and checkboxes fire the change event as soon as a selection is made, where as the other element types (textboxes & textarea) wait until they loose focus. 

Consider the following HTML
<table>
    <tr>
        <td>First Name</td>
        <td>
            <input id="txtFirstName" type="text" class="inputRequired" />
        </td>
    </tr>
    <tr>
        <td>Last Name</td>
        <td>
            <input id="txtLastName" type="text" class="inputRequired" />
        </td>
    </tr>
    <tr>
        <td>City</td>
        <td>
            <select id="ddlCity" class="inputRequired">
                <option value="Select">Select</option>
                <option value="New York">New York</option>
                <option value="London">London</option>
                <option value="Chennai">Chennai</option>
                <option value="Sydney">Sydney</option>
            </select>
        </td>
    </tr>
    <tr>
        <td>Favourite Color</td>
        <td>
            <input id="radioRed" name="color" type="radio" value="Red"
                    class="inputRequired" />Red
            <input id="radioGreen" name="color" type="radio" value="Green"
                    class="inputRequired" />Green
            <input id="radioBlue" name="color" type="radio" value="Blue"
                    class="inputRequired" />Blue
        </td>
    </tr>
    <tr>
        <td>Contact Method</td>
        <td>
            <input id="chkBoxEmail" type="checkbox" value="Email"
                    class="inputRequired" />Email
            <input id="chkBoxPhone" type="checkbox" value="Phone"
                    class="inputRequired" />Phone
            <input id="chkBoxSocialMedia" type="checkbox" value="Social Media"
                    class="inputRequired" />Social Media
        </td>
    </tr>
    <tr>
        <td>
            Comments
        </td>
        <td>
            <textarea id="txtComments" class="inputRequired"></textarea>
        </td>
    </tr>
    <tr>
        <td>
            <input id="btnSubmit" type="button" value="Submit" />
        </td>
        <td>
            <div id="divResult"></div>
        </td>
    </tr>
</table>

As soon as the selection in the dropdownlist changes, we want to handle the change event and display the selected value in the div element with id="divResult". In the example below, we are using the id selector, so only the select element change event is handled. 

jQuery change event 

$(document).ready(function () {
    $('#ddlCity').change(function () {
        var selectedValue = $(this).val();
        if (selectedValue == "Select")
            selectedValue = "Please select city";
        $('#divResult').html(selectedValue);
    });
});

The following code handles the change event of all the input elements (textbox, radio button, checkbox). Notice that in this example we are using the jquery element selector. Change event of select and textarea is not handled.

$(document).ready(function () {
    var result = '';
    $('input').change(function () {
        if (result == '') {
            result += $(this).val();
        }
        else {
            result += ', ' + $(this).val();
        }

        $('#divResult').html(result);
    });
});

The following code handles the change event of all the elements on the page. Notice that in this example we are using the jquery class selector. 

jquery dropdown change event example

$(document).ready(function () {
    var result = '';
    $('.inputRequired').change(function () {
        if (result == '') {
            result += $(this).val();
        }
        else {
            result += ', ' + $(this).val();
        }

        $('#divResult').html(result);
    });
});

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