Elemento simplifies working with Elemental2. In a nutshell Elemento brings the following features to the table:
- Type safe builders, event handlers and CSS selectors
- Helper methods to manipulate the DOM tree
- Execute asynchronous tasks in parallel, in sequence or as long as a certain condition is met.
- Simple, non-invasive, slash-based router (
/a/b/c) - Small logging wrapper around
console.logusing categories, log levels, and a predefined log format. - Ready to be used with GWT and J2CL
- Minimal dependencies
- Elemental2 1.1.0 (
elemental2-core,elemental2-domandelemental2-webstorage) - GWT project (
org.gwtproject.event:gwt-eventandorg.gwtproject.safehtml:gwt-safehtml)
- Elemental2 1.1.0 (
TOC
- Get Started
- Builder API
- Event Handlers
- Typesafe CSS Selectors
- Custom Elements
- Goodies
- SVG & MathML
- Flow
- Router
- Logger
- Samples
- Contributing
- Get Help
Elemento is available in Maven Central. The easiest way is to import its BOM
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.jboss.elemento</groupId>
<artifactId>elemento-bom</artifactId>
<version>1.4.12</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>and add a dependency to either
<dependency>
<groupId>org.jboss.elemento</groupId>
<artifactId>elemento-core</artifactId>
<type>gwt-lib</type>
</dependency>or
<dependency>
<groupId>org.jboss.elemento</groupId>
<artifactId>elemento-core</artifactId>
</dependency>depending on your stack. If you're using GWT, inherit from org.jboss.elemento.Core:
<module>
<inherits name="org.jboss.elemento.Core"/>
</module>When working with GWT Elemental it is often awkward and cumbersome to create an hierarchy of elements. Even simple structures like
<section class="main">
<input class="toggle-all" type="checkbox">
<label for="toggle-all">Mark all as complete</label>
<ul class="todo-list">
<li>
<div class="view">
<input class="toggle" type="checkbox" checked>
<label>Taste Elemento</label>
<button class="destroy"></button>
</div>
<input class="edit">
</li>
</ul>
</section>lead to a vast amount of Document.createElement() and chained Node.appendChild() calls. With Elemento creating the above structure is as easy as
import static org.jboss.elemento.Elements.*;
import static org.jboss.elemento.InputType.checkbox;
import static org.jboss.elemento.InputType.text;
HTMLElement section = section().css("main")
.add(input(checkbox).id("toggle-all").css("toggle-all"))
.add(label()
.apply(l -> l.htmlFor = "toggle-all")
.textContent("Mark all as complete"))
.add(ul().css("todo-list")
.add(li()
.add(div().css("view")
.add(input(checkbox)
.css("toggle")
.checked(true))
.add(label().textContent("Taste Elemento"))
.add(button().css("destroy")))
.add(input(text).css("edit"))))
.element();The class Elements provides convenience methods to create the most common elements. It uses a fluent API to create and append elements on the fly. Take a look at the API documentation for more details.
When creating large hierarchies of elements you often need to assign an element somewhere in the tree. Use an inline assignment together with element() to create and assign the element in one go:
import static org.jboss.elemento.Elements.*;
final HTMLElement count;
final HTMLElement footer = footer()
.add(count = span().css("todo-count").element())
.element();Elemento provides methods to easily register event handlers. There are constants for most of the known event types.
You can either add event handlers when building the element hierarchy:
import static org.jboss.elemento.Elements.*;
import static org.jboss.elemento.EventType.*;
import static org.jboss.elemento.InputType.checkbox;
import static org.jboss.elemento.InputType.text;
HTMLLIElement listItem = li()
.add(div().css("view")
.add(input(checkbox)
.css("toggle")
.on(change, event -> toggle()))
.add(label()
.textContent("Taste Elemento")
.on(dblclick, event -> edit()))
.add(button()
.css("destroy")
.on(click, event -> destroy())))
.add(input(text)
.css("edit")
.on(keydown, this::keyDown)
.on(blur, event -> blur()))
.element();or register them later using EventType.bind():
import org.gwtproject.event.shared.HandlerRegistration;
import static elemental2.dom.DomGlobal.alert;
import static org.jboss.elemento.EventType.bind;
import static org.jboss.elemento.EventType.click;
HandlerRegistration handler = bind(listItem, click, event -> alert("Clicked"));The latter approach returns org.gwtproject.event.shared.HandlerRegistration which you can use to remove the handler again.
In order to make it easier to work with keyboard events, Elemento provides an enum with the most common keyboard codes:
import elemental2.dom.KeyboardEvent;
import static org.jboss.elemento.Key.Escape;
import static org.jboss.elemento.Key.Enter;
void keyDown(KeyboardEvent event) {
if (Escape.match(event)) {
...
} else if (Enter.match(event)) {
...
}
}Elemento provides a typesafe selector API. It can be used to express simple CSS selector like .class or #id up to complex selectors like
#main [data-list-item|=foo] a[href^="http://"] > .fas.fa-check, .external[hidden]This selector can be created with
import org.jboss.elemento.By;
import static org.jboss.elemento.By.AttributeOperator.CONTAINS_TOKEN;
import static org.jboss.elemento.By.AttributeOperator.STARTS_WITH;
By selector = By.group(
By.id("main")
.desc(By.data("listItem", CONTAINS_TOKEN, "foo")
.desc(By.element("a").and(By.attribute("href", STARTS_WITH, "http://"))
.child(By.classname(new String[]{"fas", "fa-check"})))),
By.classname("external").and(By.attribute("hidden"))
);The selector can be used to find single or all HTML elements:
import org.jboss.elemento.By;
import static org.jboss.elemento.By.AttributeOperator.STARTS_WITH;
import static org.jboss.elemento.Elements.a;
import static org.jboss.elemento.Elements.body;
By selector = By.element("a").and(By.attribute("href", STARTS_WITH, "http://"));
for (HTMLElement element : body().findAll(selector)) {
a(element).css("external");
}Elemento makes it easy to create custom elements. As for Elemento custom elements are a composite of HTML elements and / or other custom elements. They're ordinary classes which can hold state or register event handlers. The only requirement is to implement IsElement<E extends HTMLElement> and return a root element:
import static org.jboss.elemento.Elements.*;
class TodoItemElement implements IsElement<HTMLElement> {
private final HTMLElement root;
private final HTMLInputElement toggle;
private final HTMLElement label;
private final HTMLInputElement summary;
TodoItemElement(TodoItem item) {
this.root = li().data("item", item.id)
.add(div().css("view")
.add(toggle = input(checkbox).css("toggle")
.checked(item.completed)
.element())
.add(label = label().textContent(item.text).element())
.add(destroy = button().css("destroy").element()))
.add(summary = input(text).css("edit").element())
.element();
this.root.classList.toggle("completed", item.completed);
}
@Override
public HTMLElement element() {
return root;
}
// event handlers omitted
}The builder API has support for IsElement<E extends HTMLElement> which makes it easy to use custom elements when building the element hierarchy:
import static org.jboss.elemento.Elements.ul;
TodoItemRepository repository = ...;
TodoItemElement[] itemElements = repository.items().stream()
.map(TodoItemElement::new)
.toArray();
ul().addAll(itemElements).element();Besides the builder API, Elemento comes with a bunch of static helper methods that roughly fall into these categories:
- Get notified when an element is attached to and detached from the DOM tree.
- Iterate over elements.
- Methods to manipulate the DOM tree (add, insert and remove elements).
- Methods to manipulate an element.
- Methods to generate safe IDs.
See the API documentation of Elements for more details.
Implement Attachable to get notified when an element is attached to and detached from the DOM tree. The attachable interface provides a static method to easily register the callbacks to attach(MutationRecord) and detach(MutationRecord):
import elemental2.dom.MutationRecord;
import org.jboss.elemento.Attachable;
import org.jboss.elemento.IsElement;
import static elemental2.dom.DomGlobal.console;
import static org.jboss.elemento.Elements.li;
class TodoItemElement implements IsElement<HTMLElement>, Attachable {
private final HTMLElement root;
TodoItemElement(TodoItem item) {
this.root = li().element();
Attachable.register(root, this);
}
@Override
public HTMLElement element() {
return root;
}
@Override
public void attach(MutationRecord mutationRecord) {
console.log("Todo item has been attached");
}
@Override
public void detach(MutationRecord mutationRecord) {
console.log("Todo item has been detached");
}
}Elemento uses the MutationObserver API to detect changes in the DOM tree and passes an MutationRecord instance to the attach(MutationRecord) and detach(MutationRecord) methods. This instance contains additional information about the DOM manipulation.
Elemento provides several methods to iterate over node lists, child elements or elements returned by a selector. There are methods which return Iterator, Iterable and Stream.
See the API documentation of Elements for more details.
Elemento comes with basic support for SVG and MathML.
To create SVG elements, add the following dependency to your POM:
<dependency>
<groupId>org.jboss.elemento</groupId>
<artifactId>elemento-svg</artifactId>
<version>1.4.12</version>
</dependency>In your GWT module inherit from org.jboss.elemento.SVG:
<module>
<inherits name="org.jboss.elemento.SVG"/>
</module>Finally, use the static methods in org.jboss.elemento.svg.SVG to create SVG elements.
To create MathML elements, add the following dependency to your POM:
<dependency>
<groupId>org.jboss.elemento</groupId>
<artifactId>elemento-mathml</artifactId>
<version>1.4.12</version>
</dependency>In your GWT module inherit from org.jboss.elemento.MathML:
<module>
<inherits name="org.jboss.elemento.MathML"/>
</module>Finally, use the static methods in org.jboss.elemento.mathml.MathML to create MathML elements.
The module elemento-flow provides a way to execute a list of asynchronous tasks in parallel or sequentially, or to execute a single task repeatedly as long as certain conditions are met.
See the API documentation of Flow for more details.
// datetime format is "2022-03-31T11:03:39.348365+02:00"
Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
.then(Response::json)
.then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
.then(context::resolve);
double ms = 500 + new Random().nextInt(2000);
Task<FlowContext> delay = context -> new Promise<>((res, __) -> setTimeout(___ -> res.onInvoke(context), ms));
// execute the two tasks in parallel
Flow.parallel(new FlowContext(), List.of(currentTime, delay))
.subscribe(context -> console.log("Current time: " + context.pop("n/a")));// datetime format is "2022-03-31T11:03:39.348365+02:00"
Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
.then(Response::json)
.then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
.then(context::resolve);
double ms = 500 + new Random().nextInt(2_000);
Task<FlowContext> delay = context -> new Promise<>((res, __) -> setTimeout(___ -> res.onInvoke(context), ms));
// execute the two tasks in sequence and cancel after 1_000 ms
Flow.parallel(new FlowContext(), List.of(currentTime, delay))
.timeout(1_000)
.subscribe(context -> console.log("Current time: " + context.pop("n/a")));Task<FlowContext> currentTime = context -> fetch("https://worldtimeapi.org/api/timezone/Europe/Berlin")
.then(Response::json)
.then(json -> Promise.resolve(Js.<JsPropertyMap<String>>cast(json).get("datetime").substring(11, 23)))
.then(context::resolve);
// fetch the current time until the milliseconds end with "0" and cancel after 5 iterations
Flow.repeat(new FlowContext(), currentTime)
.while_(context -> !context.pop("").endsWith("0"))
.iterations(5)
.subscribe(context -> console.log("Current time: " + context.pop("n/a")));Elemento offers a very basic router. The router is minimal invasive and built around a few simple concepts:
Route: Annotation that can be used to decorate pages. An annotation processor collects all classes annotated with@Routeand generates an implementation ofRoutes.Routes: Provides a map of places and their corresponding pages. This can be used to register all places in one go.Place: Data class that represents a place in an application. A place is identified by a route, and can have an optional title and a custom root element. If present the children of the root element are replaced by the elements of the page.Page: Simple interface that represents a collection of HTML elements. Implementations need to implement a single method:Iterable<HTMLElement> elements()PlaceManager: Class that keeps track of registered places, handles navigation events, and updates the DOM accordingly. The place manager can be customized using builder like methods and has astart()method to show the initial page.
See the API documentation of PlaceManager for more details.
@Route("/")
public class HomePage implements Page {
@Override
public Iterable<HTMLElement> elements() {
return singletonList(div()
.add(h(1, "Welcome"))
.add(p().textContent("Hello world!"))
.element());
}
}
public class Application {
public void entryPoint() {
body().add(div().id("main"));
new PlaceManager()
.root(By.id("main"))
.register(new Place("/"), HomePage::new)
// could also be registered with
// .register(RoutesImpl.INSTANCE.places());
.start();
}
}Elemento contains a small wrapper around console.log that uses categories, log levels, and a predefined log format.
The different log methods delegate to the corresponding methods in console:
Logger.error(String, Object... params)→console.error()Logger.warn(String, Object... params)→console.warn()Logger.info(String, Object... params)→console.info()Logger.debug(String, Object... params)→console.debug()
To get a logger use Logger.getLogger(String category).
package org.acme;
public class Foo {
private static final Logger logger = Logger.getLogger(Foo.class.getName());
}You can use an arbitrary string as category. By using a hierarchical category, you can override subcategories. String substitutions are supported, and you can pass a variable list of parameters to the log methods.
The log level is set globally for all categories using Logger.setLevel(Level level). You can override the level for one category using Logger.setLevel(String category, Level level). To reset a category, use Logger.resetLevel(String category). If the category contains ., it is interpreted hierarchically. This means that if the category org.jboss is overridden, this is also applied to all subcategories (unless overridden otherwise).
The log format is predefined as
HH:mm:ss.SSS <level> [<category>] <message>
and cannot be customized. If the category is a fully qualified class name, the package names are shortened. In any case the category is trimmed, and right aligned.
The logger module exports some methods with slightly adjusted signatures to JavaScript. You can use them for instance in the browser dev tools to control the global and category based log levels:
org.jboss.elemento.logger.Logger.setLevel(String level)- sets the global log levelorg.jboss.elemento.logger.Logger.setLevel(String category, String level)- overrides the log level for one categoryorg.jboss.elemento.logger.Logger.resetLevel(String category)- resets the log level for the category to the global log level
Please use the fully qualified name!
Elemento comes with different sample applications to showcase and test the various modules. They're available at https://hal.github.io/elemento/samples/
If you want to contribute to Elemento, please follow the steps in contribution.
If you need help feel free to contact us at Gitter, browse the API documentation or file an issue.
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