Selecting a picklist value with script does not invoke the On User Input function.

Selecting a picklist value with script does not invoke the On User Input function.

After I populate a checkbox picklist with items I am using the field.select(<value>);
The picklist has On User Input code that needs to execute on the selection.
But what I am finding is that the selection occurs but the script does not execute.

How can I progammatically invoke the On User Input function for a checkbox picklist?

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