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:
-
-
When a Boolean object is used
as the condition in a conditional test, JavaScript returns the value
of the Boolean object. For
example, a Boolean object whose
value is false is treated as the primitive value false, and a
Boolean
object whose value is true is treated as the primitive value
true in
conditional tests. If the Boolean object is a
false
object, the conditional statement evaluates to false.
-
You can use a Boolean object in place of a
Boolean primitive.
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
