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Element Properties & Attributes

Get and set DOM properties and attributes.

The Element API contains methods to update and query parts of an element. You can use the Element API to change property and attribute values for server-side elements.

About Attributes

Attributes are used mainly for the initial configuration of elements.

Attribute values are always stored as strings.

Example 1. Setting attributes for the nameField element
Source code
Java
Element nameField = ElementFactory.createInput();
nameField.setAttribute("id", "nameField");
nameField.setAttribute("placeholder", "John Doe");
nameField.setAttribute("autofocus", "");
Example 2. The same example as the previous one, expressed as HTML
Source code
HTML
<input id="nameField" placeholder="John Doe" autofocus>

You can also retrieve and manipulate attributes after they have been set.

Example 3. Retrieving and changing attributes in the nameField element
Source code
Java
// "John Doe"
String placeholder = nameField.getAttribute("placeholder");

// true
nameField.hasAttribute("autofocus");

nameField.removeAttribute("autofocus");

// ["id", "placeholder"]
nameField.getAttributeNames().toArray();

About Properties

Properties are used mainly to dynamically change the settings of an element after it has been initialized.

Any JavaScript value can be used as a property value in the browser.

You can use different variations of the Element.setProperty() method to set a property value as a String, boolean, double or JsonValue.

Example 4. Setting a property value as a double
Source code
Java
Element element = ElementFactory.createInput();
element.setProperty("value", 42.2);

Similarly, you can use different variations of the Element.getProperty() method to retrieve the value of a property as a String, boolean, double or JsonValue.

If you retrieve the value of a property as a different type from that used to set it, JavaScript type coercion rules are used to convert the value. For example, a property set as a non-empty String results as true if fetched as a boolean.

Example 5. Converting retrieved value types
Source code
Java
// Assuming the "value" property is 42.2:

// true, since any non-empty string is
// true in JavaScript
boolean helloBoolean = element.getProperty("value", true);

// 42, string is parsed to a JS number and
// truncated to an int
int helloInt = element.getProperty("value", 0);

Difference between Using Attributes and Properties

Be cautious when using attributes and properties:

  • It’s often possible to use either an attribute or property with the same name for the same effect, and both work fine.

  • However, in certain cases:

    • only one or the other works, or

    • the attribute is considered only when the element is initialized, and the property is effective after initialization.

You should always check the specific documentation for the element you are using to find out whether a feature should be configured using a property or an attribute.

Using the textContent Property

You can set an element’s textContent property using the Element.setText() method. This removes all the children of the element and replaces them with a single text node with the given value.

The ElementFactory interface provides helpers that you can use to create an element with a given text content.

Example 6. Using the createSpan() and createDiv() helper methods with the setText() method
Source code
Java
// <div>Hello world</div>
Element element = ElementFactory.createDiv("Hello world");

// <div>Hello world<span></span></div>
element.appendChild(ElementFactory.createSpan());

// <div>Replacement text</div>
element.setText("Replacement text");

To retrieve the text of an element, you can use the:

  • Element.getText() method to return the text in the element itself. Text in child elements is ignored.

  • Element.getTextRecursively() method to return the text of the entire element tree, by recursively concatenating the text from all child elements.

Example 7. Using the getText() and getTextRecursively() methods
Source code
Java
element.setText("Welcome back ");

Element name = ElementFactory.createStrong("Rudolph Reindeer");
// <div>Welcome back <strong>Rudolph
// Reindeer</strong></div>
element.appendChild(name);

// returns "Welcome back Rudolph Reindeer"
element.getTextRecursively();
// returns "Welcome back "
element.getText();

Synchronizing Properties to the Server

By default, values updated in the browser aren’t sent to the server. To synchronize a property, use the Element.addPropertyChangeListener() method. The method takes three parameters:

  1. the name of the property to synchronize;

  2. the name of the DOM event that triggers the synchronization; and

  3. a listener that is invoked when the property value changes.

After the property has been synchronized to the server, you can retrieve its value using the getProperty() method. If you don’t need to react to the property change directly when it occurs, you can use a NO-OP listener.

Example 8. Using a NO-OP listener to synchronize the value property of a text input element whenever the change event occurs
Source code
Java
textInput.addPropertyChangeListener("value", "change", e -> {});
Note
 As an alternative, you can use the addEventData() method to transfer the value from the input to the server. See Listening to Element Events for more information.
Example 9. Retrieving User Input

This example demonstrates how to use the Element API to retrieve user input. The example adds a text input field that allows the user to enter their name.

  1. Create a text input element:

    Source code
    Java
    Element textInput = ElementFactory.createInput();
textInput.setAttribute("placeholder", "Enter your name");

  2. Transfer the value to the server by asking the client to update the server-side input element every time the value changes in the browser:

    Source code
    Java
    textInput.addPropertyChangeListener("value", "change", e -> {});

  3. Retrieve the synchronized properties using Element.getProperty():

    Source code
    Java
    button.addEventListener("click", e -> {
    String responseText = "Hello " + textInput.getProperty("value"); 1
    Element response = ElementFactory.createDiv(responseText);
    getElement().appendChild(response);
});

    1. The value property is null if the property wasn’t previously set and the user hasn’t typed text into the field.

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