Decorator

As of June 2019 still experimental feature and a stage 2 proposal for Javascript.

To use, must enable 'experimentalDecorators' compiler option.

Basics

@expression declaration attached to

• class definition
• method
• accessor
• property
• parameter

The expression must evaluate a function be called at run time.

Decoration factory - just a function that returns such a function

Multiple Decorator Application Order

Decoration composition - multiple decoration acts like function composition: expression for decoration evaluated from top to down, resulted decorators are called (to decorate) from bottom to top.

Inside same class, order of application (decorate) is:

1. Parameter Decorators, followed by Method, Accessor, or Property Decorators are applied for each instance member.
2. Parameter Decorators, followed by Method, Accessor, or Property Decorators are applied for each static member.
3. Parameter Decorators are applied for the constructor.
4. Class Decorators are applied for the class.

Examples

See https://github.com/bingtimren/typescript-decorator-example/tree/master/src