Variable column name in plpgsql function

I am trying to create a trigger that needs to capture the primary key
value out of NEW variable.

However the trigger can be called from 2 different tables whose PKs are

Table1id
Table2id

Is possible to declare a variable to build the column name

Tableid varchar(20) := TG_RELNAME || ''id'';

And then use this variable to get the PK value?

Tableidvalue int4 := NEW.tableid;

Thanks,
Woody

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