How to Make Changes in Magento’s Core Functionality Without Touching its Core

Magento handles its data in a specific way as per the models and modules in its functionality.
Sometimes there might be a need to change the way this data is handled or displayed for any reason
or scenario whatsoever. Changing the Magento’s core directly is a bad practice in such cases because these changes made in the core would seize to exist when the Magento is upgraded and all the
changes would be lost for further use.

Certain ways to change Magento’s core functionality without altering the files in its core folder are:

• Plugins
• Events and observers
• Preferences

‘Plugins’ are the best way to make changes in Magento functionality. Although in some cases these
Magento Plugins do not prove to be useful, hence in such cases we use ‘Events and Observers’. In the scenarios where both Plugins and Events and Observers fail to solve the purpose, ‘Preferences’ are
used.

Plugins

Plugins were introduced in Magento 2 and did not exist in Magento 1. Plugins can be utilized for all classes but only for changing public methods. Protected and private methods cannot be modified
using Plugins. There are three types of Magento Plugins which are provided in Magento and they are:

• Before – executed right before the actual function that needs to be modified
• After – executed right after the actual function that needs to be modified
• Around – executed both before and after the actual function that needs to be modified. It
  has a callable method, where it takes a callable variable as a parameter. This variable denotes the function that is being treated. Each time this parameter is called, it returns the
  function it denotes.

Events and observers

Events and observers are a way to intercept Magento’s flow by observing the events that the Magento triggers. Observers are hooked to events in the Magento Functionality, for example, customer login. These can be used to do changes in such events, like, we can write a function for shooting an e-mail to the customer each time they log in, etc.

Preferences

Preferences in Magento 2 are similar to the rewrites in Magento
1. Preferences are used to substitute an instance of a class with another instance. It is basically used to call a substitute class instead of the original class asked for. This substitute class is the one where all the changes in functionality are done without changing anything in the original class.