ng-aspect

NgAspect 1.0 BETA

NgAspect is a little library of decorators that unlocks aspect-oriented programming features in JavaScript.

Aspect-oriented programming suggests separating cross-cutting concerns (logging, caching, monitoring, data validation, error detection and so on) from main business logic. In brief it introduces:

• advice - code implementing cross-cutting concerns
• pointcut - when code where in your main code advices shall be applied

NgAspect provides decorators @Before and @After that allow to bind an advice to a pointcut e.g. @Before( Class/Constructor, "methodName" ). It also exports @Pointcut decorator that points out what method can be supplied with advices.

How does it work?

import { Before, After, Pointcut } from "./aspect";
 
class Foo {
  @Pointcut
  bar(){
    console.log( "calling bar", arguments );
  }
}
 
class Advice {
  @Before( Foo, "bar" )
  preLog() {
    console.log( "calling pre-log", arguments );
  }
 
  @After( Foo, "bar" )
  postLog() {
    console.log( "calling post-log" );
  }
}
 
(new Foo()).bar( 1, 2, 3 );
 

Output:

calling pre-log 1,2,3
calling bar 1,2,3
calling post-log

The same goes for static methods

import { Before, After, Pointcut } from "./aspect";
 
class Foo {
  @Pointcut
  static bar(){
    console.log( "calling bar" );
  }
}
 
class Advice {
  @Before( Foo, "bar" )
  @After( Foo, "bar" )
  static log() {
    console.log( "log" );
  }
}
 
Foo.bar();
 

Syntax

Setting a single target

@Before( Foo, "bar" )
@After( Foo, "bar" )

or

@Before([ Foo, "bar" ])
@After([ Foo, "bar" ])

Setting multiple targets

@Before([
  [ Foo, "bar" ],
  [ Baz, "quiz" ],
])