Element 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.

Note
By default, values updated in the browser are not sent to the server. See Retrieving User Input for how to transfer data to the server.

About Attributes

Attributes are used mainly for the initial configuration of elements.

Attribute values are always stored as strings.

Example: Setting attributes for the nameField element.

Element nameField = ElementFactory.createInput();
nameField.setAttribute("id", "nameField");
nameField.setAttribute("placeholder", "John Doe");
nameField.setAttribute("autofocus", "");

Example: The same example as above expressed as HTML.

<input id="nameField" placeholder="John Doe" autofocus>

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

Example: Retrieving and changing attributes in the nameField element.

// "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 setProperty method to set a property value as a String, boolean, double or JsonValue.

Example: Setting a property value as a double.

Element element = ElementFactory.createInput();
element.setProperty("value", "42.2");

Similarly, you can use different variations of the 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 to that as which it was set, 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: Converting retrieved value types.

// 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);

Using Attributes Vs. Properties

Be cautious when using attributes and properties:

  • In many cases it is 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’re 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 setText method. This removes all 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: Using the createSpan and createDiv helper methods with the setText method.

// <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:

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

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

Example: Using the getText and getTextRecursively methods.

element.setText("Welcome back ");

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

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