getPrototypeOf

Summary

Returns the prototype of an object.

Syntax

Object.getPrototypeOf( object )

object: Required. The object that references the prototype.

Return Value

The prototype of the object argument. The prototype is also an object.

Examples

The following example illustrates the use of the Object.getPrototypeOf function.

// Create a constructor function.
 function Pasta(grain, width) {
     this.grain = grain;
     this.width = width;
 }
 // Create an object from the pasta constructor.
 var spaghetti = new Pasta("wheat", 0.2);

 // Obtain the prototype from the object.
 var proto = Object.getPrototypeOf(spaghetti);

 // Add a property to the prototype and validate that
 // the original object has the property.
 proto.foodgroup = "carbohydrates";
 document.write(spaghetti.foodgroup + " ");

 // Verify that the prototype obtained from the object
 // is the same as the prototype of the constructor.
 var result = (proto === Pasta.prototype);
 document.write(result + " ");

 // Verify that prototype obtained from the object
 // is a prototype of the original object.
 var result = proto.isPrototypeOf(spaghetti);
 document.write(result);

 // Output: carbohydrates true true

The following example uses the Object.getPrototypeOf function to validate data types.

var reg = /a/;
 var result = (Object.getPrototypeOf(reg) === RegExp.prototype);
 document.write(result + " ");

 var err = new Error("an error");
 var result = (Object.getPrototypeOf(err) === Error.prototype);
 document.write(result);

 // Output: true true

Exceptions

If the object argument is not an object, a TypeError exception is thrown.

Microsoft Developer Network: Article