Quick start

Installation

npm

npm i @aspectjs/common @aspectjs/core

yarn

yarn add @aspectjs/common @aspectjs/core

Configuration

AspectJS is based on the tc39 experimental decorators draft 2. Support for this feature have to be enabled in your tsconfig.json:

tsconfig.json

{
  "compilerOptions": {
    "experimentalDecorators": true
  }
}

How to use

1. Create your own annotation

Simply put, an annotation is an ES decorator with no behavior. Annotations act as markers to identify specific elements in your codebase where an aspect can be applied.

log-errors.annotation.ts

import { AnnotationFactory } from '@aspectjs/common';

// Create an annotation
export const LogErrors = new AnnotationFactory('demo').create(
  function LogErrors() {},
);

2. Create your own aspect

log-errors.aspect.ts

import { AfterThrow, AfterThrowContext, Aspect, on } from '@aspectjs/core';

@Aspect()
export class LogErrorsAspect {
  @AfterThrow(
    on.classes.withAnnotations(LogErrors),
    on.methods.withAnnotations(LogErrors),
  )
  logAround(context: AfterThrowContext, error: Error) {
    console.error(
      `${context.target}(${context.args.join(',')}) throwed error ${error}`,
    );
    // Propagate the error
    throw error;
  }
}

3. Enable an aspect

aop.ts

import { getWeaver } from '@aspectjs/core';

getWeaver().enable(new LogErrorsAspect());

4. Use the annotation in your code

hello.ts

@LogErrors()
export class Hello {
  hello: string;

  constructor(hello: string = 'hello') {
    this.hello = hello;
  }

  @LogErrors()
  sayHello(who: string = 'world') {
    throw new Error(`${this.hello} ${who}`);
  }
}