Class based components with hooks, reactive state and concurrent mode

The Odoo Web Library (OWL) is a smallish (~<20kb gzipped) UI framework intended to be the basis for the Odoo Web Client. Owl is a modern framework, written in Typescript, taking the best ideas from React and Vue in a simple and consistent way. Owl's main features are:

• a declarative component system,
• a reactivity system based on hooks,
• a store implementation (for state management),
• a small frontend router

Owl components are defined with ES6 classes, they use QWeb templates, an underlying virtual dom, integrates beautifully with hooks, and the rendering is asynchronous.

Try it online! An online playground is available at https://odoo.github.io/owl/playground to let you experiment with the Owl framework. There are some code examples to showcase some interesting features.

Owl is currently mostly stable. Possible future changes are explained in the roadmap.

Here is a short example to illustrate interactive components:

const { Component, useState } = owl;
const { xml } = owl.tags;

class Counter extends Component {
  static template = xml`
    <button t-on-click="state.value++">
      Click Me! [<t t-esc="state.value"/>]
    </button>`;

  state = useState({ value: 0 });
}

class App extends Component {
  static template = xml`
    <div>
      <span>Hello Owl</span>
      <Counter />
    </div>`;

  static components = { Counter };
}

const app = new App();
app.mount(document.body);

Note that the counter component is made reactive with the useState hook. Also, all examples here uses the xml helper to define inline templates. But this is not mandatory, many applications will load templates separately.

More interesting examples can be found on the playground application.

OWL is designed to be used in highly dynamic applications where changing requirements are common and code needs to be maintained by large teams.

• XML based: templates are based on the XML format, which allows interesting applications. For example, they could be stored in a database and modified dynamically with xpaths.
• templates compilation in the browser: this may not be a good fit for all applications, but if you need to generate dynamically user interfaces in the browser, this is very powerful. For example, a generic form view component could generate a specific form user interface for each various models, from a XML view.
• no toolchain required: this is extremely useful for some applications, if, for various reasons (security/deployment/dynamic modules/specific assets tools), it is not ok to use standard web tools based on npm.

Owl is not designed to be fast nor small (even though it is quite good on those two topics). It is a no nonsense framework to build applications. There is only one way to define components (with classes).

If you are interested in a comparison with React or Vue, you will find some more information here.

A complete documentation for Owl can be found here:

• Main documentation page.

The most important sections are:

• Tutorial: TodoList application
• QWeb templating language
• Component
• Hooks

Found an issue in the documentation? A broken link? Some outdated information? Submit a PR!

Owl can be installed with the following command:

npm install @odoo/owl

If you want to use a simple <script> tag, the last release can be downloaded here:

• owl-1.0.4.js
• owl-1.0.4.min.js

Some npm scripts are available:

Owl components in an application are used to define a (dynamic) tree of components.

        Root
        /   \
       A     B
      / \
     C   D

State: each component can manage its own local state. It is a simple ES6 class, there are no special rules:

class Counter extends Component {
  static template = xml`
    <button t-on-click="increment">
      Click Me! [<t t-esc="state.value"/>]
    </button>`;

  state = { value: 0 };

  increment() {
    this.state.value++;
    this.render();
  }
}

The example above shows a component with a local state. Note that since there is nothing magical to the state object, we need to manually call the render function whenever we update it. This can quickly become annoying (and not efficient if we do it too much). There is a better way: using the useState hook, which transforms an object into a reactive version of itself:

const { useState } = owl.hooks;

class Counter extends Component {
  static template = xml`
    <button t-on-click="increment">
      Click Me! [<t t-esc="state.value"/>]
    </button>`;

  state = useState({ value: 0 });

  increment() {
    this.state.value++;
  }
}

Note that the t-on-click handler can even be replaced by an inline statement:

    <button t-on-click="state.value++">

Props: sub components often needs some information from their parents. This is done by adding the required information to the template. This will then be accessible by the sub component in the props object. Note that there is an important rule here: the information contained in the props object is not owned by the sub component, and should never be modified.

class Child extends Component {
  static template = xml`<div>Hello <t t-esc="props.name"/></div>`;
}

class Parent extends Component {
  static template = xml`
    <div>
        <Child name="'Owl'" />
        <Child name="'Framework'" />
    </div>`;
  static components = { Child };
}

Communication: there are multiple ways to communicate information between components. However, the two most important ways are the following:

• from parent to children: by using props,
• from a children to one of its parent: by triggering events.

The following example illustrate both mechanisms:

class OrderLine extends Component {
  static template = xml`
    <div t-on-click="add">
        <div><t t-esc="props.line.name"/></div>
        <div>Quantity: <t t-esc="props.line.quantity"/></div>
    </div>`;

  add() {
    this.trigger("add-to-order", { line: props.line });
  }
}

class Parent extends Component {
  static template = xml`
    <div t-on-add-to-order="addToOrder">
        <OrderLine
            t-foreach="orders"
            t-as="line"
            line="line" />
    </div>`;
  static components = { OrderLine };
  orders = useState([{ id: 1, name: "Coffee", quantity: 0 }, { id: 2, name: "Tea", quantity: 0 }]);

  addToOrder(event) {
    const line = event.detail.line;
    line.quantity++;
  }
}

In this example, the OrderLine component trigger a add-to-order event. This will generate a DOM event which will bubble along the DOM tree. It will then be intercepted by the parent component, which will then get the line (from the detail key) and then increment its quantity. See the section on event handling for more details on how events work.

Note that this example would have also worked if the OrderLine component directly modifies the line object. However, this is not a good practice: this only works because the props object received by the child component is reactive, so the child component is then coupled to the parents implementation.

OWL is LGPL licensed.