TypeScript · Interface

PropertyDescriptor

PropertyDescriptor is the descriptor parameter used in TypeScript's documented method-decorator example. It represents runtime metadata for the decorated member and is passed after the target and property key.

How it works

PropertyDescriptor is a JavaScript runtime descriptor object used in decorator-style code to describe a property or method. TypeScript documentation shows it as the descriptor parameter received alongside the target and property key in a method decorator example.

Syntax

function LogMethod(target: any, propertyKey: string | symbol, descriptor: PropertyDescriptor)

Parameters

Name	Type	Description
`target`	`any`	The object or class prototype containing the decorated member; the page's example types this as any.
`propertyKey`	`string \| symbol`	The decorated property's name, represented as a string or symbol.
`descriptor`	`PropertyDescriptor`	The runtime descriptor for the decorated property or method.

Key points

A method-decorator-style function can receive a PropertyDescriptor as its third parameter.
The descriptor is a runtime value that can be inspected inside the decorator function.
The official page presents PropertyDescriptor in the context of decorator metadata configuration.

Common mistakes

The documented decorator example belongs to experimental decorator metadata support; using metadata-related behavior may require the reflect-metadata module.

Example: Passing a method descriptor

function LogMethod(target: object, propertyKey: string | symbol, descriptor: PropertyDescriptor) {
  console.log(target, propertyKey, descriptor);
}

class Demo {
  foo(bar: number) {}
}

const descriptor = Object.getOwnPropertyDescriptor(Demo.prototype, "foo");
if (descriptor) LogMethod(Demo.prototype, "foo", descriptor);

The example passes a method's runtime property descriptor to a decorator-style function.

When to use it

Method decorators

Inspect a decorated class method's runtime metadata.

Decorator callbacks

Pass a member descriptor into decorator logic.

Decorator metadata workflows

View emitted decorator-related metadata in generated JavaScript.

decorators
emitDecoratorMetadata
reflect-metadata
propertyKey

Source: TSConfig Option: emitDecoratorMetadata. Checked 2026-10-15.