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on

on messageName [parameterList]
    statements
end messageName

The on keyword defines a new message handler of the specified name.

The optional parameterList lets the handler receive values sent along with a message. HyperCard assigns each value to a parameter variable in the parameterList.

Demo Script

on mouseUp
   flashTheButton "bkgnd btn id 57",2
 end mouseUp
 

 on flashTheButton whichBtn, howMany
   repeat for (howMany * 2) times
     set the hilite of whichBtn to not the hilite of whichBtn
   end repeat
 end flashTheButton

Placeholders

messageName
Any text string, without quotation marks, that represents the name of the message handler you want to write:

calculateDebt
selectWholeLine

As in:

on calculateDebt
on selectWholeLine theLine, aContainer

parameterList
A comma-separated list of local variable names.

The actual names don’t matter as long as they’re not the same as one of HyperCard’s reserved words. (That is, don’t use result as a variable name.) For example:

var1
var1,var2,var3, var4
fieldName, N, numberOfCharacters

statements
Any return-separated list of built-in commands, user-defined handlers, or keywords that are part of a message or function handler.

put "Hello world"   -- built-in command
get total(field 1)  -- function call
global HelpInfo     -- keyword

Related Topics

• exit
• Handling messages
• param
• paramCount
• params
• pass
• result
• return
• send
• target
• The message-passing order
• Using parameter variables
• What are messages?
• Writing message handlers

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