# 🦉 Config 🦉

The Owl framework is designed to work in many situations. However, it is
sometimes necessary to customize some behaviour. This is done by using the
global `config` object. It currently has two keys:

- [`mode`](#mode),
- [`env`](#env).

## Mode

By default, Owl is in _production_ mode, this means that it will try to do its
job fast, and skip some expensive operations. However, it is sometimes necessary
to have better information on what is going on, this is the purpose
of the `dev` mode.

Owl has a mode flag, in `owl.config.mode`. Its default value is `prod`, but
it can be set to `dev`:

```js
owl.config.mode = "dev";
```

Note that templates compiled with the `prod` settings will not be recompiled.
So, changing this setting is best done at startup.

An important job done by the `dev` mode is to validate props for each component
creation and update. Also, extra props will cause an error.

## Env

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

Whenever a root component is mounted, Owl will take the environment from
`owl.config.env` and use it to setup the component (and its children).

- if no environment was setup, an empty environment will be generated,
- if an environment exists, but does not have a QWeb key, a new QWeb instance
  will then be added to the environment.

The correct way to customize an environment is to simply modify `owl.config.env`
before the first component is created:

```js
owl.config.env = {
    _t: myTranslateFunction,
    user: {...},
    services: {
        ...
    },
};
const app = new App();
app.mount(document.body);
```