Name
Object.isPrototypeOf() — is one object the prototype of another?
Synopsis
object
.
isPrototypeOf
(
o
)
Arguments
o
Any object.
Returns
true
if
object
is the prototype of
o
; false
if o
is
not an object or if object
is not the
prototype of o
.
Description
As explained in Chapter 9, JavaScript objects
inherit properties from their prototype object. The prototype of an
object is referred to by the prototype
property of the constructor
function that creates and initializes the object. The isPrototypeOf()
method provides a way to
determine if one object is the prototype of another. This technique
can be used to determine the class of an object.
Example
var
o
=
new
Object
();
// Create an object
Object
.
prototype
.
isPrototypeOf
(
o
)
// true: o is an object
Function
.
prototype
.
isPrototypeOf
(
o
.
toString
);
// true: toString is a function
Array
.
prototype
.
isPrototypeOf
([
1
,
2
,
3
]);
// true: [1,2,3] is an array
// Here is a way to perform a similar test
(
o
.
constructor
==
Object
);
// true: o was created with Object() constructor
(
o
.
toString
.
constructor
==
Function
);
// true: o.toString is a function
// Prototype objects themselves have prototypes. The following call
// returns true, showing that function objects inherit properties
// from Function.prototype and also from Object.prototype.
Object
.
prototype
.
isPrototypeOf
(
Function
.
prototype
);
See Also
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