Name
Object.constructor — an object’s constructor function
Synopsis
object
.
constructor
Description
The constructor
property of
any object is a reference to the function that was used as the
constructor for that object. For example, if you create an array
a
with the Array()
constructor, a.constructor
is an Array:
a
=
new
Array
(
1
,
2
,
3
);
// Create an object
a
.
constructor
==
Array
// Evaluates to true
One common use of the constructor
property is to determine the
type of unknown objects. Given an unknown value, you can use the
typeof
operator to determine
whether it is a primitive value or an object. If it is an object,
you can use the constructor
property to determine what type of object it is. For example, the
following function determines whether a given value is an
array:
function
isArray
(
x
)
{
return
((
typeof
x
==
"object"
)
&&
(
x
.
constructor
==
Array
));
}
Note, however, that while this technique works for the objects
built into core JavaScript, it is not guaranteed to work with host
objects such as the Window object of client-side JavaScript. The
default implementation of the Object.toString()
method provides another
way to determine the type of an unknown object.
See Also
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