documentation/content/developer/reference/frontend/javascript_modules.rst

.. _frontend/js_modules:

==================
Javascript Modules
==================

Odoo supports three different kinds of javascript files:

- :ref:`plain javascript files <frontend/modules/plain_js>` (no module system),
- :ref:`native javascript module <frontend/modules/native_js>`.
- :ref:`Odoo modules <frontend/modules/odoo_module>` (using a custom module system),

As described in the :ref:`assets management page <reference/assets>`,
all javascript files are bundled together and served to the browser.
Note that native javascript files are processed by the Odoo server and transformed into Odoo custom modules.

Let us briefly explain the purpose behind each kind of javascript file. Plain
javascript files should be reserved only for external libraries and some small
specific low level purposes. All new javascript files should be created in the
native javascript module system. The custom module system is only useful for old,
not yet converted files.

.. _frontend/modules/plain_js:

Plain Javascript files
======================

Plain javascript files can contain arbitrary content. It is advised to use the
*iife* :dfn:`immediately invoked function execution` style when writing such a file:

.. code-block:: javascript

  (function () {
    // some code here
    let a = 1;
    console.log(a);
  })();

The advantages of such files is that we avoid leaking local variables to the
global scope.

Clearly, plain javascript files do not offer the benefits of a module system, so
one needs to be careful about the order in the bundle (since the browser will
execute them precisely in that order).

.. note::
  In Odoo, all external libraries are loaded as plain javascript files.

.. _frontend/modules/native_js:

Native Javascript Modules
=========================

Most new Odoo javascript code should use the native javascript module system. This
is simpler, and brings the benefits of a better developer experience with a better
integration with the IDE.

There is a very important point to know: Odoo needs to know which files
should be translated into :ref:`Odoo modules <frontend/modules/odoo_module>` and which
files should not be translated. This is an opt-in system: Odoo will look at the
first line of a JS file and check if it contains the string *@odoo-module*. If so, it will
automatically be converted to an Odoo module.

For example, let us consider the following module, located in :file:`web/static/src/file_a.js`:

.. code-block:: javascript

  /** @odoo-module **/
  import { someFunction } from './file_b';

  export function otherFunction(val) {
      return someFunction(val + 3);
  }

Note the comment in the first line: it describes that this file should be converted.
Any file without this comment will be kept as-is (which will most likely be an
error). This file will then be translated into an Odoo module that look like this:

.. code-block:: javascript

   odoo.define('@web/file_a', function (require) {
   'use strict';
   let __exports = {};

   const { someFunction } = require("@web/file_b");

   __exports.otherFunction = function otherFunction(val) {
       return someFunction(val + 3);
   };

   return __exports;
   )};

So, as you can see, the transformation is basically adding `odoo.define` on top,
and updating the import/export statements.

Another important point is that the translated module has an official name:
*@web/file_a*. This is the actual name of the module. Every relative imports
will be converted as well. Every file located in an Odoo addon
:file:`some_addon/static/src/path/to/file.js` will be assigned a name prefixed by the
addon name like this: *@some_addon/path/to/file*.

Relative imports work, but only if the modules are in the same Odoo addon. So, imagine that we have
the following file structure:

::

  addons/
      web/
          static/
              src/
                  file_a.js
                  file_b.js
      stock/
          static/
              src/
                  file_c.js

The file :file:`file_b` can import :file:`file_a` like this:

.. code-block:: javascript

  /** @odoo-module **/
  import {something} from `./file_a`

But :file:`file_c` need to use the full name:

.. code-block:: javascript

  /** @odoo-module **/
  import {something} from `@web/file_a`


Aliased modules
---------------

Because :ref:`Odoo modules <frontend/modules/odoo_module>` follow a different module naming pattern, a system exists to allow a smooth
transition towards the new system. Currently, if a file is converted to a module (and therefore
follow the new naming convention), other files not yet converted to ES6-like syntax in the project
won't be able to require the module. Aliases are here to map old names with new ones by creating a
small proxy function. The module can then be called by its new *and* old name.

To add such alias, the comment tag on top of the file should look like this:

.. code-block:: javascript

  /** @odoo-module alias=web.someName**/
  import { someFunction } from './file_b';

  export default function otherFunction(val) {
      return someFunction(val + 3);
  }

Then, the translated module will also create an alias with the requested name:

.. code-block:: javascript

  odoo.define(`web.someName`, function(require) {
      return require('@web/file_a')[Symbol.for("default")];
  });

The default behaviour of aliases is to re-export the ``default`` value of the
module they alias. This is because "classic" modules generally export a single
value which would be used directly, roughly matching the semantics of default
exports.
However it is also possible to delegate more directly, and follow the exact
behaviour of the aliased module:

.. code-block:: javascript

  /** @odoo-module alias=web.someName default=0**/
  import { someFunction } from './file_b';

  export function otherFunction(val) {
      return someFunction(val + 3);
  }

In that case, this will define an alias with exactly the values exported by the
original module:

.. code-block:: javascript

  odoo.define(`web.someName`, function(require) {
      return require('@web/file_a');
  });

.. note::
   Only one alias can be defined using this method. If you were to need another one to have, for
   example, three names to call the same module, you would have to add a proxy manually.
   This is not good practice and should be avoided unless there is no other options.

Limitations
-----------

For performance reasons, Odoo does not use a full javascript
parser to transform native modules. There are, therefore, a number of limitations including but not
limited to:

- an `import` or `export` keyword cannot be preceded by a non-space character,
- a multiline comment or string cannot have a line starting by `import` or `export`

  .. code-block:: javascript

    // supported
    import X from "xxx";
    export X;
      export default X;
        import X from "xxx";

    /*
     * import X ...
     */

    /*
     * export X
     */


    // not supported

    var a= 1;import X from "xxx";
    /*
      import X ...
    */

- when you export an object, it can't contain a comment

  .. code-block:: javascript

      // supported
      export {
        a as b,
        c,
        d,
      }

      export {
        a
      } from "./file_a"


      // not supported
      export {
        a as b, // this is a comment
        c,
        d,
      }

      export {
        a /* this is a comment */
      } from "./file_a"

- Odoo needs a way to determine if a module is described by a path (like :file:`./views/form_view`)
  or a name (like `web.FormView`). It has to use a heuristic to do just that: if there is a `/` in
  the name, it is considered a path.  This means that Odoo does not really support module names with
  a `/` anymore.

As "classic" modules are not deprecated and there is currently no plan to remove them, you can and should keep using
them if you encounter issues with, or are constrained by the limitations of, native modules. Both styles can coexist
within the same Odoo addon.


.. _frontend/modules/odoo_module:

Odoo Module System
==================

Odoo has defined a small module system (located in the file
:file:`addons/web/static/src/js/boot.js`, which needs to be loaded first). The Odoo
module system, inspired by AMD, works by defining the function `define`
on the global odoo object. We then define each javascript module by calling that
function.  In the Odoo framework, a module is a piece of code that will be executed
as soon as possible.  It has a name and potentially some dependencies.  When its
dependencies are loaded, a module will then be loaded as well.  The value of the
module is then the return value of the function defining the module.

As an example, it may look like this:

.. code-block:: javascript

    // in file a.js
    odoo.define('module.A', function (require) {
        "use strict";

        var A = ...;

        return A;
    });

    // in file b.js
    odoo.define('module.B', function (require) {
        "use strict";

        var A = require('module.A');

        var B = ...; // something that involves A

        return B;
    });

An alternative way to define a module is to give explicitly a list of dependencies
in the second argument.

.. code-block:: javascript

    odoo.define('module.Something', ['module.A', 'module.B'], function (require) {
        "use strict";

        var A = require('module.A');
        var B = require('module.B');

        // some code
    });


If some dependencies are missing/non ready, then the module will simply not be
loaded.  There will be a warning in the console after a few seconds.

Note that circular dependencies are not supported. It makes sense, but it means that one
needs to be careful.

Defining a module
-----------------

The `odoo.define` method is given three arguments:

- `moduleName`: the name of the javascript module.  It should be a unique string.
  The convention is to have the name of the odoo addon followed by a specific
  description. For example, `web.Widget` describes a module defined in the `web`
  addon, which exports a `Widget` class (because the first letter is capitalized)

  If the name is not unique, an exception will be thrown and displayed in the
  console.

- `dependencies`: the second argument is optional. If given, it should be a list
  of strings, each corresponding to a javascript module.  This describes the
  dependencies that are required to be loaded before the module is executed. If
  the dependencies are not explicitly given here, then the module system will
  extract them from the function by calling toString on it, then using a regexp
  to find all the `require` statements.

  .. code-block:: javascript

     odoo.define('module.Something', ['web.ajax'], function (require) {
         "use strict";

         var ajax = require('web.ajax');

         // some code here
         return something;
     });

- finally, the last argument is a function which defines the module. Its return
  value is the value of the module, which may be passed to other modules requiring
  it.  Note that there is a small exception for asynchronous modules, see the
  next section.

If an error happens, it will be logged (in debug mode) in the console:

* `Missing dependencies`:
  These modules do not appear in the page. It is possible that the JavaScript
  file is not in the page or that the module name is wrong
* `Failed modules`:
  A javascript error is detected
* `Rejected modules`:
  The module returns a rejected Promise. It (and its dependent modules) is not
  loaded.
* `Rejected linked modules`:
  Modules who depend on a rejected module
* `Non loaded modules`:
  Modules who depend on a missing or a failed module

Asynchronous modules
--------------------

It can happen that a module needs to perform some work before it is ready.  For
example, it could do an rpc to load some data.  In that case, the module can
simply return a promise. The module system will simply
wait for the promise to complete before registering the module.

.. code-block:: javascript

    odoo.define('module.Something', function (require) {
        "use strict";

        var ajax = require('web.ajax');

        return ajax.rpc(...).then(function (result) {
            // some code here
            return something;
        });
    });