Introduction

Cross-platform dart:html that works in the browser, Dart VM, and Flutter.

Typical use cases are:

• Cross-platform application development (e.g. Flutter mobile and web versions).
• Web crawling and scraping

The project is licensed under the Apache License 2.0. Some of the source code was adopted from the original dart:html, which is documented in the relevant files.

Contributing

• This project welcomes all sorts of contributions. You don't need to be an expert.
• Found a bug? Proposing something? Create an issue.
• Have a contribution? Create a pull request.

Similar projects?

• universal_io (cross-platform dart:io)
• jsdom (DOM implementation in Javascript).

Getting started

1. Add dependency

In pubspec.yaml:

dependencies:
  universal_html: ^1.1.4

Now you can replace usage of "dart:html" with "package:universal_html/html.dart".

2. Choose library

Option 1

import 'package:universal_html/prefer_sdk/html.dart';

This library exports dart:html by default. The library exports our implementation only when dart:io is available.

If you use this library, your package will not compile in Node.JS. Dart tools may also mistakenly think that your package is not compatible with VM/Flutter.

Option 2

import 'package:universal_html/prefer_universal/html.dart';

This library exports our implementation by default. The library exports dart:html only in browsers.

Getting warnings? In some cases, when you mix universal_io classes with dart:html classes, your IDE produces type warnings ("universal_html Element is not dart:html Element"). Your application should still compile (in Dart2js, universal_html classes will be dart:html classes).

Proposed future method

Dart SDK feature request #37232 proposes that developers could supply missing dart:html in VM/Flutter in pubspec.yaml.

3. That's it!

import "package:universal_html/html.dart";

void main() {
  // Create a DOM tree
  final divElement = new DivElement();
  divElement.append(new Element.tag("h1")
    ..classes.add("greeting")
    ..appendText("Hello world!"));

  // Print outer HTML
  print(divElement.outerHtml);
  // --> <div><h1>Hello world</h1></div>

  // Do a CSS query
  print(divElement.querySelector("div > .greeting").text);
  // --> Hello world
}

Manual

Server-side rendering

The package comes with ServerSideRenderer, which is a web server for rendering your web application in the server-side.

import 'package:universal_html/driver.dart';
import 'package:universal_html/html.dart';

void main() {
  final renderer = new ServerSideRenderer(webAppMain);
  renderer.bind("localhost", 12345);
}

void webAppMain() {
  document.body.appendText("Hello world!");
}

Creating and using browser simulators

import 'package:universal_html/driver.dart';
import 'package:universal_html/html.dart';

Future main() async {
  // Construct a driver
  final driver = new HtmlDriver(userAgent:"My Hacker News bot");
  
  // Load a document.
  await driver.setDocumentFromUri(Uri.parse("https://news.ycombinator.com/"));
  
  // Select top story
  final topStoryTitle = driver.document.querySelectorAll(".athing > .title").first.text;
  print("Top Hacker News story is: ${topStoryTitle}");
}

Implemented APIs

Strategy

• Our goal is that universal_html behaves identically to dart:html running in Chrome.
• DIFFERENCES.md contains an automatically generated list of dart:html APIs that are not yet declared by this package yet.
• Some APIs are declared, but not implemented. These will either throw UnimplementedError or (when appropriate) fail silently.

HTML

• Document nodes
  • All core classes (Node, Element, etc.)
  • All HtmlElement subclasses (AnchorElement, ResetButtonElement, etc.)
  • Most class members. For example, anchorElement.href returns the resolved URI. Only a few class members are still missing (see DIFFERENCES.md).
• DOM parsing
  • You can parse HTML/XML with innerHtml/outerHtml setters and DomParser
  • HTML parsing uses package:html
  • CSS parsing uses package:csslib
  • XML parsing uses package:xml
• DOM printing
  • element.innerHtml, element.outerHtml
• DOM events
  • For example, element.onClick.listen(...) receives invocation of element.click().

CSS

• Much of the CSS classes (CssStyleDeclaration, etc.)
• CSS queries
  • Methods element.querySelector(..), element.querySelectorAll(..), element.matchesSelector(..)
  • Element name (table)
  • Element ID (#id)
  • Element class (.classA.classB)
  • Combinators:
    • element.class#id
    • s0 s1 s2
    • s0 s1 s2
    • s0 > s1 > s2
    • s0 ~ s1 ~ s2
    • s0 + s1 + s2
  • Pseudoselectors:
    • :disabled
    • :first-child
    • :last-child
    • :not(x)
    • :nth-child(5)
    • :nth-child(even)
    • :nth-child(3n+1)
    • :only-child
    • :root
  • Attribute selectors:
    • [name]
    • [name=value]
    • [name~=value]
    • [name|=value]
    • [name^=value]
    • [name$=value]
    • [name*=value]

Layout

Currently, the library does not attempt to calculate layout for the elements.

Every DOM element has a private field RenderData, which you can get with BrowserImplementationUtils.getRenderData(...)). When a property such as element.offset is called, the RenderData instance is responsible for evaluating the answer. The default implementation generally returns 0. If you want to implement layout engine, you can override BrowserImplementation.newRenderData(element).

Networking

• Form submitting
  • Implemented and tested, but doesn't support all encodings yet.
  • Ways to use:
    • formElement.submit()
    • submitButtonElement.click()
• HttpRequest (XMLHttpRequest)
  • Implemented and tested.
• EventSource ("application/event-stream" client)
  • Implemented and tested.

Currently, networking classes don't implement same-origin policies, CORS, and other security specifications. We hope to fix this in future.

Nevigator

• locale
• All APIs are declared

Window

• console
• history
  • back(...), pushState(...), etc.
• location
  • origin, href, etc.
• localStorage / sessionStorage
  • Implemented and tested.
  • Stores values in the heap.
• All APIs are declared.

Other SDK libraries

We wrote mock implementation of the following SDK libraries:

• dart:indexed_db
• dart:js
• dart:js_util
• dart:svg
• dart:web_gl

Any attempt to use these APIs will ead to UnimplementedException. The libraries are available in:

• package:universal_html/(libraryName).dart
• package:universal_html/prefer_sdk/(libraryName).dart
• package:universal_html/prefer_universal/(libraryName).dart