owl/doc/reference/environment.md

🦉 Environment 🦉

Content

• Overview
• Setting an Environment
• Using a sub environment
• Content of an Environment
• Special keys

Overview

An environment is an object which contains a QWeb instance. Whenever a root component is created, it is assigned an environment (see below for more info on this). This environment is then automatically given to each sub component (and accessible in the this.env property).

    Root
    /  \
   A    B

This way, all components share the same QWeb instance. Owl internally requires that the environment has a qweb key which maps to a QWeb instance. This is the QWeb instance that will be used to render each templates in this specific component tree. Note that if no QWeb instance is provided, Owl will simply generate it on the fly.

The environment is mostly static. Each application is free to add anything to the environment, which is very useful, since this can be accessed by each sub component.

Setting an environment

An Owl application needs an environment to be executed. The environment has an important key: the QWeb instance, which will render all templates.

Whenever a root component App is mounted, Owl will setup a valid environment by following the next steps:

• take the env object defined on App.env (if no env was explicitly setup, this will return the empty env object defined on Component)
• if env.qweb is not set, then Owl will create a QWeb instance.

The correct way to customize an environment is to simply set it up on the root component class, before the first component is created:

const env = {
    _t: myTranslateFunction,
    user: {...},
    services: {
        ...
    },
};
mount(App, { target: document.body, env });

It is also possible to simply share an environment between all root components, by simply doing this:

Component.env = myEnv; // will be the default env for all components

Note that this environment is the global owl environment for an application. The next section explains how to extend an environment for a specific sub component and its children.

Using a sub environment

It is sometimes useful to add one (or more) specific keys to the environment, from the perspective of a specific component and its children. In that case, the solution presented above will not work, since it sets the global environment.

There is a hook for this situation: useSubEnv.

class FormComponent extends Component {
  constructor(parent, props) {
    super(parent, props);
    useSubEnv({ myKey: someValue });
  }
}

Content of an Environment

Some good use cases for additional keys in the environment are:

• some configuration keys,
• session information,
• generic services (such as doing rpcs).

Doing it this way means that components are easily testable: we can simply create a test environment with mock services.

For example:

async function myEnv() {
  const templates = await loadTemplates();
  const qweb = new QWeb({ templates });
  const session = getSession();

  return {
    _t: myTranslateFunction,
    session: session,
    qweb: qweb,
    services: {
      localStorage: localStorage,
      rpc: rpc,
    },
    debug: false,
    inMobileMode: true,
  };
}

async function start() {
  const env = await myEnv();
  mount(App, { target: document.body, env });
}

Special Keys

There are two special key/value added by Owl if not provided in the environment: the QWeb instance and a browser object:

• qweb will be set to an empty QWeb instance. This is absolutely necessary for Owl to be able to render anything
• browser: this is an object that contains some common access points to the browser methods with a side effect. See browser for more information. Note that the browser object will be removed from the environment in Owl 2.0.