Flash CS3 Documentation

Learning ActionScript 2.0 in Adobe Flash > Data and Data Types > About data types > About primitive and complex data types > null data type

null data type

The null data type has only one value, null. This value means no value--that is, a lack of data. You can assign the null value in a variety of situations to indicate that a property or variable does not yet have a value assigned to it. For example, you can assign the null value in the following situations:

• To indicate that a variable exists but has not yet received a value
• To indicate that a variable exists but no longer contains a value
• As the return value of a function, to indicate that no value was available to be returned by the function
• As a parameter to a function, to indicate that a parameter is being omitted

Several methods and functions return null if no value has been set. The following example demonstrates how you can use null to test if form fields currently have form focus:

if (Selection.getFocus() == null) {
    trace("no selection");
}

Flash CS3