Execution Context In Dynamics 365 CRM/CE And How To Pass It To the Java Script Function

Execution Context is passing the complete information and data of the record to the Java Script function, From this execution context you can get the information of the form by using the getFormContext() method.

To use this executionContext you have to declare java script function with one parameter as executionContext.
If you want tot perform the operation on Form data you have to get the Form Context from this executionContext as executionContext.getFormContext(); 

To pass this executionContext from the form you have to check the checkbox as :
Pass execution context ass first parameter.

From Classic View Form:

Open the form => Form properties => Add Event

From Power Apps View Form:
Open the form => Events => Open Event Handler.