ActionScript for Flash MX: The Definitive Guide, Second Edition

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Chapter 9: Functions

value of function2(). Because objects are passed by reference, we can pass a function

identifier to another function and it will arrive unscathed. The passed function can

be executed like this:

function doCommand (command) {

command( ); // Executes the passed function

}

// Some examples:

doCommand(stop); // Pass the built-in stop() function (stops current movie)

doCommand(play); // Pass the built-in play() function (plays current movie)

We can use this technique to assign a callback function to a series of text field

objects:

function initFormFields (fields, callbackFunc) {

// Set focus callback functions for text fields.

for (var i = 0; i < fields.length; i++) {

fields[i].onSetFocus = callbackFunc;

}

}

// Create a list of the text fields.

editFields = [firstNameField, lastNameField, emailField,

phoneField, companyField, commentsField];

// Function that colors a text field blue.

function handleFieldFocus ( ) {

this.background = true;

this.backgroundColor = 0x333399;

}

initFormFields(editFields, handleFieldFocus);

Storing Functions in Variables

Because functions are a type of object, we can treat them as we treat any other data.

In the following example, we assign the built-in gotoAndPlay function to the variable

gp, which gives us a shorter way to refer to the function: ...