How does it work?

Explanation of Mosaic's work mechanics

This article mostly is for the contributors who are willing to enhance the Mosaic's core package's (@tilework/mosaic) behaviour with additional functionality.

Read the code for more information, or feel free to use our Github Discussions to ask us for specifics!

Features

middleware - a method to attach a namespace to a piece of functionality and ensure the plugins work for that namespace

Extensible - a method to ensure proper context during the construction of the given class. Important for interception of class properties being declared with class property syntax during their initialisation in the constructor

setPlugins - a method that accepts an array of modules (which are .plugin.js files), sets the internal property and exposes it to the window object.

How ?

The middleware function wraps functionality (further - "middlewarable") into a Proxy, and assigns a namespace to it.

If the middlewarable is a function

When it is called, the following happens:

  1. The plugins are being extracted from the lib/plugins/plugin-storage

  2. These plugins are wrapped around the initial function, thus generating a new function

  3. This function is called on the original arguments

If the middlewarable is a class

During the new call, the following happens:

  1. Extensible ensures that the instance is a Proxy from the very beginning, this Proxy intercepts all members' accesses and applies plugins on the fly

  2. All of the member-property plugins are applied to it, replacing the original properties with the ones the plugins result into.

Afterwards, when the object is used, the following happens:

  1. When calling any member of the instance, the plugin storage is scanned for the plugins for that member, and if any are found - they are applied to the callable member before executing it

Also, the following is applied to the class itself

  1. The class itself is a Proxy, to ensure that calls to static properties are handled as member properties - by immediate replacement. It is a proxy only when is accessed from within its instance, otherwise it is not a proxy.

If the middlewarable is a primitive

This is not supported

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