Core JavaScript Reference 1.5: | 2 | WebReference

Core JavaScript Reference 1.5: | 2

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Core JavaScript Reference 1.5





Boolean

The Boolean object is an object wrapper for a boolean value.


Core object  

 

Implemented in  

JavaScript 1.1, NES 2.0

JavaScript 1.3: added toSource method  

ECMA version  

ECMA-262  


Created by
The Boolean constructor:

new Boolean(value)


Parameters


value

 

The initial value of the Boolean object. The value is converted to a boolean value, if necessary. If value is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (""), the object has an initial value of false. All other values, including any object or the string "false", create an object with an initial value of true.  


Description
Do not confuse the primitive Boolean values true and false with the true and false values of the Boolean object.

Any object whose value is not undefined or null, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example, the condition in the following if statement evaluates to true:

x = new Boolean(false);
if(x) //the condition is true

This behavior does not apply to Boolean primitives. For example, the condition in the following if statement evaluates to false:

x = false;
if(x) //the condition is false

Do not use a Boolean object to convert a non-boolean value to a boolean value. Instead, use Boolean as a function to perform this task:

x = Boolean(expression) //preferred
x = new Boolean(expression) //don't use

If you specify any object, including a Boolean object whose value is false, as the initial value of a Boolean object, the new Boolean object has a value of true.

myFalse=new Boolean(false)   // initial value of false
g=new Boolean(myFalse)       //initial value of true
myString=new String("Hello") // string object
s=new Boolean(myString)      //initial value of true

Do not use a Boolean object in place of a Boolean primitive.


Backward Compatibility

JavaScript 1.2 and earlier versions. The Boolean object behaves as follows:


Property Summary


Property

Description

constructor

 

Specifies the function that creates an object's prototype.  

prototype

 

Defines a property that is shared by all Boolean objects.  


Method Summary


Method

Description

toSource

 

Returns an object literal representing the specified Boolean object; you can use this value to create a new object. Overrides the Object.toSource method.  

toString

 

Returns a string representing the specified object. Overrides the Object.toString method.  

valueOf

 

Returns the primitive value of a Boolean object. Overrides the Object.valueOf method.  

In addition, this object inherits the watch and unwatch methods from Object.


Examples
The following examples create Boolean objects with an initial value of false:

bNoParam = new Boolean()
bZero = new Boolean(0)
bNull = new Boolean(null)
bEmptyString = new Boolean("")
bfalse = new Boolean(false)

The following examples create Boolean objects with an initial value of true:

btrue = new Boolean(true)
btrueString = new Boolean("true")
bfalseString = new Boolean("false")
bSuLin = new Boolean("Su Lin")


constructor

Specifies the function that creates an object's prototype. Note that the value of this property is a reference to the function itself, not a string containing the function's name.



Property of  

Boolean  

Implemented in  

JavaScript 1.1, NES 2.0  

ECMA version  

ECMA-262  


Description
See Object.constructor.


prototype

Represents the prototype for this class. You can use the prototype to add properties or methods to all instances of a class. For information on prototypes, see Function.prototype.



Property of  

Boolean  

Implemented in  

JavaScript 1.1, NES 2.0  

ECMA version  

ECMA-262  


toSource

Returns a string representing the source code of the object.



Method of  

Boolean  

Implemented in  

JavaScript 1.3  


Syntax
toSource()


Parameters
None


Description
The toSource method returns the following values:

This method is usually called internally by JavaScript and not explicitly in code.


See also
Object.toSource


toString

Returns a string representing the specified Boolean object.



Method of  

Boolean  

Implemented in  

JavaScript 1.1, NES 2.0  

ECMA version  

ECMA-262  


Syntax
toString()


Parameters
None.


Description
The Boolean object overrides the toString method of the Object object; it does not inherit Object.toString. For Boolean objects, the toString method returns a string representation of the object.

JavaScript calls the toString method automatically when a Boolean is to be represented as a text value or when a Boolean is referred to in a string concatenation.

For Boolean objects and values, the built-in toString method returns the string "true" or "false" depending on the value of the boolean object. In the following code, flag.toString returns "true".

var flag = new Boolean(true)
var myVar=flag.toString()


See also
Object.toString


valueOf

Returns the primitive value of a Boolean object.



Method of  

Boolean  

Implemented in  

JavaScript 1.1  

ECMA version  

ECMA-262  


Syntax
valueOf()


Parameters
None


Description
The valueOf method of Boolean returns the primitive value of a Boolean object or literal Boolean as a Boolean data type.

This method is usually called internally by JavaScript and not explicitly in code.


Examples
x = new Boolean();
myVar=x.valueOf()      //assigns false to myVar


See also
Object.valueOf


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Last Updated May 19, 2003