In the custom action settings page, we have the “Variables” button in the “What Actions to Execute” section (See screenshot below).
In designer custom action, 'Variable' is available in custom action ribbon as shown below
Clicking the “Variables” button opens a dialog that shows existing variable definitions along with “New Variable” button (See screenshot below).
Clicking on the “New Variable” button opens a dialog and prompt to enter the variable name and default value (see screenshot below).
Variable Name: Specify a name for Variable. This name will be used in the later actions to access the value that we store in this Variable.
Default Value:
Value that we are going to store in the variable. It can be empty, literal value (string), placeholder from current list item and value returned by a function.
Note: Variable names should be unique
Example:
Variable Name: varUsers
Default Value: Supports following types
•Literal/Custom values
•Another field value (Place holders of current list item)
•Functions (Takes place holders of current list item as possible arguments)