Returns a Boolean value that indicates whether or not an object is an instance of a particular class or constructed function.
object instanceof class |
Arguments
- object
-
Required. Any object expression.
- class
-
Required. Any object class or constructed function.
Remarks
The instanceof operator returns true if object is an instance of class or constructed function. It returns false if object is not an instance of the specified class or function, or if object is null.
The JScript Object is special. An object is only considered an instance of Object if and only if the object was constructed with the Object constructor.
Example 1
The following example illustrates a use of the instanceof operator to check the type of a variable.
В | Copy Code |
---|---|
// This program uses System.DateTime, which must be imported. import System function isDate(ob) : String { if (ob instanceof Date) return "It's a JScript Date" if (ob instanceof DateTime) return "It's a .NET Framework Date" return "It's not a date" } var d1 : DateTime = DateTime.Now var d2 : Date = new Date print(isDate(d1)) print(isDate(d2)) |
The output of this code is:
В | Copy Code |
---|---|
It's a .NET Date It's a JScript Date |
Example 2
The following example illustrates a use of the instanceof operator to check instances of a constructed function.
В | Copy Code |
---|---|
function square(x : int) : int { return x*x } function bracket(s : String) : String{ return("[" + s + "]"); } var f = new square print(f instanceof square) print(f instanceof bracket) |
The output of this code is:
В | Copy Code |
---|---|
true false |
Example 3
The following example illustrates how the instanceof operator checks if objects are instances of Object.
В | Copy Code |
---|---|
class CDerived extends Object { var x : double; } var f : CDerived = new CDerived; var ob : Object = f; print(ob instanceof Object); ob = new Object; print(ob instanceof Object); |
The output of this code is:
В | Copy Code |
---|---|
false true |