Data types

A data type defines a set of values. For example, the Boolean data type is the set of exactly two values: true and false. In addition to the Boolean data type, ActionScript 3.0 defines several more commonly used data types, such as String, Number, and Array. You can define your own data types by using classes or interfaces to define a custom set of values. All values in ActionScript 3.0, whether they are primitive or complex, are objects.

A primitive value is a value that belongs to one of the following data types: Boolean, int, Number, String, and uint. Working with primitive values is usually faster than working with complex values, because ActionScript stores primitive values in a special way that makes memory and speed optimizations possible.

Note: For readers interested in the technical details, ActionScript stores primitive values internally as immutable objects. The fact that they are stored as immutable objects means that passing by reference is effectively the same as passing by value. This cuts down on memory usage and increases execution speed, because references are usually significantly smaller than the values themselves.

A complex value is a value that is not a primitive value. Data types that define sets of complex values include Array, Date, Error, Function, RegExp, XML, and XMLList.

Many programming languages distinguish between primitive values and their wrapper objects. Java, for example, has an int primitive and the java.lang.Integer class that wraps it. Java primitives are not objects, but their wrappers are, which makes primitives useful for some operations, and wrapper objects better suited for other operations. In ActionScript 3.0, primitive values and their wrapper objects are, for practical purposes, indistinguishable. All values, even primitive values, are objects. The runtime treats these primitive types as special cases that behave like objects but that don’t require the normal overhead associated with creating objects. This means that the following two lines of code are equivalent:

var someInt:int = 3; 
var someInt:int = new int(3);

All the primitive and complex data types listed above are defined by the ActionScript 3.0 core classes. The core classes allow you to create objects using literal values instead of using the new operator. For example, you can create an array using a literal value or the Array class constructor, as follows:

var someArray:Array = [1, 2, 3]; // literal value 
var someArray:Array = new Array(1,2,3); // Array constructor

Type checking

Type checking can occur at either compile time or run time. Statically typed languages, such as C++ and Java, do type checking at compile time. Dynamically typed languages, such as Smalltalk and Python, handle type checking at run time. As a dynamically typed language, ActionScript 3.0 has run-time type checking, but also supports compile-time type checking with a special compiler mode called strict mode. In strict mode, type checking occurs at both compile time and run time, but in standard mode, type checking occurs only at run time.

Dynamically typed languages offer tremendous flexibility when you structure your code, but at the cost of allowing type errors to manifest at run time. Statically typed languages report type errors at compile time, but at the cost of requiring that type information be known at compile time.

Compile-time type checking

Compile-time type checking is often favored in larger projects because as the size of a project grows, data type flexibility usually becomes less important than catching type errors as early as possible. This is why, by default, the ActionScript compiler in Flash Professional and Flash Builder is set to run in strict mode.

Adobe Flash Builder

You can disable strict mode in Flash Builder through the ActionScript compiler settings in the Project Properties dialog box.

To provide compile-time type checking, the compiler needs to know the data type information for the variables or expressions in your code. To explicitly declare a data type for a variable, add the colon operator (:) followed by the data type as a suffix to the variable name. To associate a data type with a parameter, use the colon operator followed by the data type. For example, the following code adds data type information to the xParam parameter, and declares a variable myParam with an explicit data type:

function runtimeTest(xParam:String) 
{ 
    trace(xParam); 
} 
var myParam:String = "hello"; 
runtimeTest(myParam);

In strict mode, the ActionScript compiler reports type mismatches as compiler errors. For example, the following code declares a function parameter xParam, of type Object, but later attempts to assign values of type String and Number to that parameter. This produces a compiler error in strict mode.

function dynamicTest(xParam:Object) 
{ 
    if (xParam is String) 
    { 
        var myStr:String = xParam; // compiler error in strict mode 
        trace("String: " + myStr); 
    } 
    else if (xParam is Number) 
    { 
        var myNum:Number = xParam; // compiler error in strict mode 
        trace("Number: " + myNum); 
    } 
}

Even in strict mode, however, you can selectively opt of out compile-time type checking by leaving the right side of an assignment statement untyped. You can mark a variable or expression as untyped by either omitting a type annotation, or using the special asterisk (*) type annotation. For example, if the xParam parameter in the previous example is modified so that it no longer has a type annotation, the code compiles in strict mode:

function dynamicTest(xParam) 
{ 
    if (xParam is String) 
    { 
        var myStr:String = xParam; 
        trace("String: " + myStr); 
    } 
    else if (xParam is Number) 
    { 
        var myNum:Number = xParam; 
        trace("Number: " + myNum); 
    } 
} 
dynamicTest(100) 
dynamicTest("one hundred");

Run-time type checking

Run-time type checking occurs in ActionScript 3.0 whether you compile in strict mode or standard mode. Consider a situation in which the value 3 is passed as an argument to a function that expects an array. In strict mode, the compiler will generate an error, because the value 3 is not compatible with the data type Array. If you disable strict mode, and run in standard mode, the compiler does not complain about the type mismatch, but run-time type checking results in a run-time error.

The following example shows a function named typeTest() that expects an Array argument but is passed a value of 3. This causes a run-time error in standard mode, because the value 3 is not a member of the parameter’s declared data type (Array).

function typeTest(xParam:Array) 
{ 
    trace(xParam); 
} 
var myNum:Number = 3; 
typeTest(myNum);  
// run-time error in ActionScript 3.0 standard mode

There may also be situations where you get a run-time type error even when you are operating in strict mode. This is possible if you use strict mode, but opt out of compile-time type checking by using an untyped variable. When you use an untyped variable, you are not eliminating type checking but rather deferring it until run time. For example, if the myNum variable in the previous example does not have a declared data type, the compiler cannot detect the type mismatch, but the code will generate a run-time error because it compares the run-time value of myNum, which is set to 3 as a result of the assignment statement, with the type of xParam, which is set to the Array data type.

function typeTest(xParam:Array) 
{ 
    trace(xParam); 
} 
var myNum = 3; 
typeTest(myNum);  
// run-time error in ActionScript 3.0

Run-time type checking also allows more flexible use of inheritance than does compile-time checking. By deferring type checking to run time, standard mode allows you to reference properties of a subclass even if you upcast. An upcast occurs when you use a base class to declare the type of a class instance but use a subclass to instantiate it. For example, you can create a class named ClassBase that can be extended (classes with the final attribute cannot be extended):

class ClassBase 
{ 
}

You can subsequently create a subclass of ClassBase named ClassExtender, which has one property named someString, as follows:

class ClassExtender extends ClassBase 
{ 
    var someString:String; 
}

Using both classes, you can create a class instance that is declared using the ClassBase data type, but instantiated using the ClassExtender constructor. An upcast is considered a safe operation, because the base class does not contain any properties or methods that are not in the subclass.

var myClass:ClassBase = new ClassExtender();

A subclass, however, does contain properties or methods that its base class does not. For example, the ClassExtender class contains the someString property, which does not exist in the ClassBase class. In ActionScript 3.0 standard mode, you can reference this property using the myClass instance without generating a compile-time error, as shown in the following example:

var myClass:ClassBase = new ClassExtender(); 
myClass.someString = "hello"; 
// no error in ActionScript 3.0 standard mode

The is operator

The is operator allows you to test whether a variable or expression is a member of a given data type. In previous versions of ActionScript, the instanceof operator provided this functionality, but in ActionScript 3.0 the instanceof operator should not be used to test for data type membership. The is operator should be used instead of the instanceof operator for manual type checking, because the expression x instanceof y merely checks the prototype chain of x for the existence of y (and in ActionScript 3.0, the prototype chain does not provide a complete picture of the inheritance hierarchy).

The is operator examines the proper inheritance hierarchy and can be used to check not only whether an object is an instance of a particular class, but also whether an object is an instance of a class that implements a particular interface. The following example creates an instance of the Sprite class named mySprite and uses the is operator to test whether mySprite is an instance of the Sprite and DisplayObject classes, and whether it implements the IEventDispatcher interface:

var mySprite:Sprite = new Sprite(); 
trace(mySprite is Sprite); // true 
trace(mySprite is DisplayObject);// true 
trace(mySprite is IEventDispatcher); // true

The is operator checks the inheritance hierarchy and properly reports that mySprite is compatible with the Sprite and DisplayObject classes (the Sprite class is a subclass of the DisplayObject class). The is operator also checks whether mySprite inherits from any classes that implement the IEventDispatcher interface. Because the Sprite class inherits from the EventDispatcher class, which implements the IEventDispatcher interface, the is operator correctly reports that mySprite implements the same interface.

The following example shows the same tests from the previous example, but with instanceof instead of the is operator. The instanceof operator correctly identifies that mySprite is an instance of Sprite or DisplayObject, but it returns false when used to test whether mySprite implements the IEventDispatcher interface.

trace(mySprite instanceof Sprite); // true 
trace(mySprite instanceof DisplayObject);// true 
trace(mySprite instanceof IEventDispatcher); // false

The as operator

The as operator also allows you to check whether an expression is a member of a given data type. Unlike the is operator, however, the as operator does not return a Boolean value. Rather, the as operator returns the value of the expression instead of true, and null instead of false. The following example shows the results of using the as operator instead of the is operator in the simple case of checking whether a Sprite instance is a member of the DisplayObject, IEventDispatcher, and Number data types.

var mySprite:Sprite = new Sprite(); 
trace(mySprite as Sprite);                 // [object Sprite] 
trace(mySprite as DisplayObject);                 // [object Sprite] 
trace(mySprite as IEventDispatcher);                 // [object Sprite] 
trace(mySprite as Number);                                       // null

When you use the as operator, the operand on the right must be a data type. An attempt to use an expression other than a data type as the operand on the right will result in an error.

Dynamic classes

A dynamic class defines an object that can be altered at run time by adding or changing properties and methods. A class that is not dynamic, such as the String class, is a sealed class. You cannot add properties or methods to a sealed class at run time.

You create dynamic classes by using the dynamic attribute when you declare a class. For example, the following code creates a dynamic class named Protean:

dynamic class Protean 
{ 
    private var privateGreeting:String = "hi"; 
    public var publicGreeting:String = "hello"; 
    function Protean() 
    { 
        trace("Protean instance created"); 
    } 
}

If you later instantiate an instance of the Protean class, you can add properties or methods to it outside the class definition. For example, the following code creates an instance of the Protean class and adds a property named aString and a property named aNumber to the instance:

var myProtean:Protean = new Protean(); 
myProtean.aString = "testing"; 
myProtean.aNumber = 3; 
trace(myProtean.aString, myProtean.aNumber); // testing 3

Properties that you add to an instance of a dynamic class are run-time entities, so any type checking is done at run time. You cannot add a type annotation to a property that you add in this manner.

You can also add a method to the myProtean instance by defining a function and attaching the function to a property of the myProtean instance. The following code moves the trace statement into a method named traceProtean():

var myProtean:Protean = new Protean(); 
myProtean.aString = "testing"; 
myProtean.aNumber = 3; 
myProtean.traceProtean = function () 
{ 
    trace(this.aString, this.aNumber); 
}; 
myProtean.traceProtean(); // testing 3

Methods created in this way, however, do not have access to any private properties or methods of the Protean class. Moreover, even references to public properties or methods of the Protean class must be qualified with either the this keyword or the class name. The following example shows the traceProtean() method attempting to access the private and public variables of the Protean class.

myProtean.traceProtean = function () 
{ 
    trace(myProtean.privateGreeting); // undefined 
    trace(myProtean.publicGreeting); // hello 
}; 
myProtean.traceProtean();

Data type descriptions

The primitive data types include Boolean, int, Null, Number, String, uint, and void. The ActionScript core classes also define the following complex data types: Object, Array, Date, Error, Function, RegExp, XML, and XMLList.

Boolean data type

The Boolean data type includes two values: true and false. No other values are valid for variables of Boolean type. The default value of a Boolean variable that has been declared but not initialized is false.

int data type

The int data type is stored internally as a 32-bit integer and includes the set of integers from

-2,147,483,648 (-231) to 2,147,483,647 (231 - 1), inclusive. Previous versions of ActionScript offered only the Number data type, which was used for both integers and floating-point numbers. In ActionScript 3.0, you now have access to low-level machine types for 32-bit signed and unsigned integers. If your variable does not need floating-point numbers, using the int data type instead of the Number data type is faster and more efficient.

For integer values outside the range of the minimum and maximum int values, use the Number data type, which can handle values between positive and negative 9,007,199,254,740,992 (53-bit integer values). The default value for variables that are of the data type int is 0.

Null data type

The Null data type contains only one value, null. This is the default value for the String data type and all classes that define complex data types, including the Object class. None of the other primitive data types, such as Boolean, Number, int, and uint, contain the value null. At run time, the value null is converted to the appropriate default value if you attempt to assign null to variables of type Boolean, Number, int, or uint. You cannot use this data type as a type annotation.

Number data type

In ActionScript 3.0, the Number data type can represent integers, unsigned integers, and floating-point numbers. However, to maximize performance, you should use the Number data type only for integer values larger than the 32-bit int and uint types can store or for floating-point numbers. To store a floating-point number, include a decimal point in the number. If you omit a decimal point, the number is stored as an integer.

The Number data type uses the 64-bit double-precision format as specified by the IEEE Standard for Binary Floating-Point Arithmetic (IEEE-754). This standard dictates how floating-point numbers are stored using the 64 available bits. One bit is used to designate whether the number is positive or negative. Eleven bits are used for the exponent, which is stored as base 2. The remaining 52 bits are used to store the significand (also called the mantissa), which is the number that is raised to the power indicated by the exponent.

By using some of its bits to store an exponent, the Number data type can store floating-point numbers significantly larger than if it used all of its bits for the significand. For example, if the Number data type used all 64 bits to store the significand, it could store a number as large as 265 - 1. By using 11 bits to store an exponent, the Number data type can raise its significand to a power of 21023.

The maximum and minimum values that the Number type can represent are stored in static properties of the Number class called Number.MAX_VALUE and Number.MIN_VALUE.

Number.MAX_VALUE == 1.79769313486231e+308 
Number.MIN_VALUE == 4.940656458412467e-324

Although this range of numbers is enormous, the cost of this range is precision. The Number data type uses 52 bits to store the significand, with the result that numbers that require more than 52 bits to represent precisely, such as the fraction 1/3, are only approximations. If your application requires absolute precision with decimal numbers, you need to use software that implements decimal floating-point arithmetic as opposed to binary floating-point arithmetic.

When you store integer values with the Number data type, only the 52 bits of the significand are used. The Number data type uses these 52 bits and a special hidden bit to represent integers from -9,007,199,254,740,992 (-253) to 9,007,199,254,740,992 (253).

The NaN value is not only used as the default value for variables of type Number, but also as the result of any operation that should return a number but does not. For example, if you attempt to calculate the square root of a negative number, the result is NaN. Other special Number values include positive infinity and negative infinity.

Note: The result of division by 0 is only NaN if the divisor is also 0. Division by 0 produces infinity when the dividend is positive or -infinity when the dividend is negative.

String data type

The String data type represents a sequence of 16-bit characters. Strings are stored internally as Unicode characters, using the UTF-16 format. Strings are immutable values, just as they are in the Java programming language. An operation on a String value returns a new instance of the string. The default value for a variable declared with the String data type is null. The value null is not the same as the empty string (""). The value null means that the variable has no value stored in it, while the empty string means that the variable has a value that is a String containing no characters.

uint data type

The uint data type is stored internally as a 32-bit unsigned integer and includes the set of integers from 0 to 4,294,967,295 (232 - 1), inclusive. Use the uint data type for special circumstances that call for non-negative integers. For example, you must use the uint data type to represent pixel color values, because the int data type has an internal sign bit that is not appropriate for handling color values. For integer values larger than the maximum uint value, use the Number data type, which can handle 53-bit integer values. The default value for variables that are of data type uint is 0.

void data type

The void data type contains only one value, undefined. In previous versions of ActionScript, undefined was the default value for instances of the Object class. In ActionScript 3.0, the default value for Object instances is null. If you attempt to assign the value undefined to an instance of the Object class, the value is converted to null. You can only assign a value of undefined to variables that are untyped. Untyped variables are variables that either lack any type annotation, or use the asterisk (*) symbol for type annotation. You can use void only as a return type annotation.

Object data type

The Object data type is defined by the Object class. The Object class serves as the base class for all class definitions in ActionScript. The ActionScript 3.0 version of the Object data type differs from that of previous versions in three ways. First, the Object data type is no longer the default data type assigned to variables with no type annotation. Second, the Object data type no longer includes the value undefined, which used to be the default value of Object instances. Third, in ActionScript 3.0, the default value for instances of the Object class is null.

In previous versions of ActionScript, a variable with no type annotation was automatically assigned the Object data type. This is no longer true in ActionScript 3.0, which now includes the idea of a truly untyped variable. Variables with no type annotation are now considered untyped. If you prefer to make it clear to readers of your code that your intention is to leave a variable untyped, you can use the asterisk (*) symbol for the type annotation, which is equivalent to omitting a type annotation. The following example shows two equivalent statements, both of which declare an untyped variable x:

var x 
var x:*

Only untyped variables can hold the value undefined. If you attempt to assign the value undefined to a variable that has a data type, the runtime converts the value undefined to the default value of that data type. For instances of the Object data type, the default value is null, which means that if you attempt to assign undefined to an Object instance the value is converted to null.

Type conversions

A type conversion is said to occur when a value is transformed into a value of a different data type. Type conversions can be either implicit or explicit. Implicit conversion, which is also called coercion, is sometimes performed at run time. For example, if the value 2 is assigned to a variable of the Boolean data type, the value 2 is converted to the Boolean value true before assigning the value to the variable. Explicit conversion, which is also called casting, occurs when your code instructs the compiler to treat a variable of one data type as if it belongs to a different data type. When primitive values are involved, casting actually converts values from one data type to another. To cast an object to a different type, you wrap the object name in parentheses and precede it with the name of the new type. For example, the following code takes a Boolean value and casts it to an integer:

var myBoolean:Boolean = true; 
var myINT:int = int(myBoolean); 
trace(myINT); // 1

Implicit conversions

Implicit conversions happen at run time in a number of contexts:

  • In assignment statements

  • When values are passed as function arguments

  • When values are returned from functions

  • In expressions using certain operators, such as the addition (+) operator

    For user-defined types, implicit conversions succeed when the value to be converted is an instance of the destination class or a class that derives from the destination class. If an implicit conversion is unsuccessful, an error occurs. For example, the following code contains a successful implicit conversion and an unsuccessful implicit conversion:

    class A {} 
    class B extends A {} 
     
    var objA:A = new A(); 
    var objB:B = new B(); 
    var arr:Array = new Array(); 
     
    objA = objB; // Conversion succeeds. 
    objB = arr; // Conversion fails.

    For primitive types, implicit conversions are handled by calling the same internal conversion algorithms that are called by the explicit conversion functions.

Explicit conversions

It’s helpful to use explicit conversions, or casting, when you compile in strict mode, because there may be times when you do not want a type mismatch to generate a compile-time error. This may be the case when you know that coercion will convert your values correctly at run time. For example, when working with data received from a form, you may want to rely on coercion to convert certain string values to numeric values. The following code generates a compile-time error even though the code would run correctly in standard mode:

var quantityField:String = "3"; 
var quantity:int = quantityField; // compile time error in strict mode

If you want to continue using strict mode, but would like the string converted to an integer, you can use explicit conversion, as follows:

var quantityField:String = "3"; 
var quantity:int = int(quantityField); // Explicit conversion succeeds.

Casting to int, uint, and Number

You can cast any data type into one of the three number types: int, uint, and Number. If the number can’t be converted for some reason, the default value of 0 is assigned for the int and uint data types, and the default value of NaN is assigned for the Number data type. If you convert a Boolean value to a number, true becomes the value 1 and false becomes the value 0.

var myBoolean:Boolean = true; 
var myUINT:uint = uint(myBoolean); 
var myINT:int = int(myBoolean); 
var myNum:Number = Number(myBoolean); 
trace(myUINT, myINT, myNum); // 1 1 1 
myBoolean = false; 
myUINT = uint(myBoolean); 
myINT = int(myBoolean); 
myNum = Number(myBoolean); 
trace(myUINT, myINT, myNum); // 0 0 0

String values that contain only digits can be successfully converted into one of the number types. The number types can also convert strings that look like negative numbers or strings that represent a hexadecimal value (for example, 0x1A). The conversion process ignores leading and trailing white space characters in the string value. You can also cast strings that look like floating-point numbers using Number(). The inclusion of a decimal point causes uint() and int() to return an integer, truncating the decimal and the characters following it. For example, the following string values can be cast into numbers:

trace(uint("5")); // 5 
trace(uint("-5")); // 4294967291. It wraps around from MAX_VALUE 
trace(uint(" 27 ")); // 27 
trace(uint("3.7")); // 3 
trace(int("3.7")); // 3 
trace(int("0x1A")); // 26 
trace(Number("3.7")); // 3.7

String values that contain non-numeric characters return 0 when cast with int() or uint() and NaN when cast with Number(). The conversion process ignores leading and trailing white space, but returns 0 or NaN if a string has white space separating two numbers.

trace(uint("5a")); // 0 
trace(uint("ten")); // 0 
trace(uint("17 63")); // 0

In ActionScript 3.0, the Number() function no longer supports octal, or base 8, numbers. If you supply a string with a leading zero to the ActionScript 2.0 Number() function, the number is interpreted as an octal number, and converted to its decimal equivalent. This is not true with the Number() function in ActionScript 3.0, which instead ignores the leading zero. For example, the following code generates different output when compiled using different versions of ActionScript:

trace(Number("044"));  
// ActionScript 3.0 44 
// ActionScript 2.0 36

Casting is not necessary when a value of one numeric type is assigned to a variable of a different numeric type. Even in strict mode, the numeric types are implicitly converted to the other numeric types. This means that in some cases, unexpected values may result when the range of a type is exceeded. The following examples all compile in strict mode, though some generate unexpected values:

var myUInt:uint = -3; // Assign int/Number value to uint variable 
trace(myUInt); // 4294967293 
 
var myNum:Number = sampleUINT; // Assign int/uint value to Number variable 
trace(myNum) // 4294967293 
 
var myInt:int = uint.MAX_VALUE + 1; // Assign Number value to uint variable 
trace(myInt); // 0 
 
myInt = int.MAX_VALUE + 1; // Assign uint/Number value to int variable 
trace(myInt); // -2147483648

The following table summarizes the results of casting to the Number, int, or uint data type from other data types.

Data type or value

Result of conversion to Number, int, or uint

Boolean

If the value is true, 1; otherwise, 0.

Date

The internal representation of the Date object, which is the number of milliseconds since midnight January 1, 1970, universal time.

null

0

Object

If the instance is null and converted to Number, NaN; otherwise, 0.

String

A number if the string can be converted to a number; otherwise, NaN if converted to Number, or 0 if converted to int or uint.

undefined

If converted to Number, NaN; if converted to int or uint, 0.

Casting to Boolean

Casting to Boolean from any of the numeric data types (uint, int, and Number) results in false if the numeric value is 0, and true otherwise. For the Number data type, the value NaN also results in false. The following example shows the results of casting the numbers -1, 0, and 1:

var myNum:Number; 
for (myNum = -1; myNum<2; myNum++) 
{ 
    trace("Boolean(" + myNum +") is " + Boolean(myNum)); 
}

The output from the example shows that, of the three numbers, only 0 returns a value of false:

Boolean(-1) is true 
Boolean(0) is false 
Boolean(1) is true

Casting to Boolean from a String value returns false if the string is either null or an empty string (""). Otherwise, it returns true.

var str1:String; // Uninitialized string is null. 
trace(Boolean(str1)); // false 
 
var str2:String = ""; // empty string 
trace(Boolean(str2)); // false 
 
var str3:String = " "; // white space only 
trace(Boolean(str3)); // true

Casting to Boolean from an instance of the Object class returns false if the instance is null; otherwise, it returns true:

var myObj:Object; // Uninitialized object is null. 
trace(Boolean(myObj)); // false 
 
myObj = new Object(); // instantiate  
trace(Boolean(myObj)); // true

Boolean variables get special treatment in strict mode in that you can assign values of any data type to a Boolean variable without casting. Implicit coercion from all data types to the Boolean data type occurs even in strict mode. In other words, unlike almost all other data types, casting to Boolean is not necessary to avoid strict mode errors. The following examples all compile in strict mode and behave as expected at run time:

var myObj:Object = new Object(); // instantiate  
var bool:Boolean = myObj; 
trace(bool); // true 
bool = "random string"; 
trace(bool); // true 
bool = new Array(); 
trace(bool); // true 
bool = NaN; 
trace(bool); // false

The following table summarizes the results of casting to the Boolean data type from other data types:

Data type or value

Result of conversion to Boolean

String

false if the value is null or the empty string (""); true otherwise.

null

false

Number, int, or uint

false if the value is NaN or 0; true otherwise.

Object

false if the instance is null; true otherwise.

Casting to String

Casting to the String data type from any of the numeric data types returns a string representation of the number. Casting to the String data type from a Boolean value returns the string "true" if the value is true, and returns the string "false" if the value is false.

Casting to the String data type from an instance of the Object class returns the string "null" if the instance is null. Otherwise, casting to the String type from the Object class returns the string "[object Object]" .

Casting to String from an instance of the Array class returns a string made up of a comma-delimited list of all the array elements. For example, the following cast to the String data type returns one string containing all three elements of the array:

var myArray:Array = ["primary", "secondary", "tertiary"]; 
trace(String(myArray)); // primary,secondary,tertiary

Casting to String from an instance of the Date class returns a string representation of the date that the instance contains. For example, the following example returns a string representation of the Date class instance (the output shows result for Pacific Daylight Time):

var myDate:Date = new Date(2005,6,1); 
trace(String(myDate)); // Fri Jul 1 00:00:00 GMT-0700 2005

The following table summarizes the results of casting to the String data type from other data types.

Data type or value

Result of conversion to string

Array

A string made up of all array elements.

Boolean

"true" or "false"

Date

A string representation of the Date object.

null

"null"

Number, int, or uint

A string representation of the number.

Object

If the instance is null, "null"; otherwise, "[object Object]".