G-L > instanceof

instanceof

instanceof

Availability

Flash Player 6.

Usage

object instanceof class

Parameters

object An ActionScript object.

class A reference to an ActionScript constructor function, such as String or Date.

Returns

If object is an instance of class, instanceof returns true; otherwise, instanceof returns false.

Description

Operator; determines whether an object belongs to a specified class. Tests if object is an instance of class.

An ActionScript object is said to be an instance of a class if the constructor function's prototype object is in the ActionScript object's prototype chain.

The instanceof operator does not convert primitive types to wrapper objects. For example, the following code returns true:

new String("Hello") instanceof String

Whereas the following code returns false:

"Hello" instanceof String

Example

To illustrate the algorithm of the instanceof operator, the following example shows how the instanceof operator might look if it was coded as an ActionScript function.

function instanceof (theObject, theClass){
	while ((theObject = theObject.__proto__) != null) {
           if (theObject == theClass.prototype) {
                  return true;
           }
	}
	return false;
}

See also

typeof