aspect.js

Introduction

Library for aspect-oriented programming with JavaScript, which takes advantage of ECMAScript 2016 decorators syntax.

NOTE: if you are using aspect.js in a plain JavaScript project that uses @babel/plugin-proposal-decorators, you must set its legacy property to true until #72 is fixed. See this migration note for more information. A sample project using JavaScript with Node >=10.12.0 (or >=8.12.0) & Babel 7.x can be found at https://github.com/matthewadams/aspect.js-babel7-poc. It's a good way to get going quickly with aspect.js in that environment.

For further reading on decorators, take a look at the spec.

Blog post, introduction to the AOP and the library could be found here.

Talk from AngularConnect.

Sample usage

import {beforeMethod, Advised, Metadata} from 'aspect.js';

class LoggerAspect {
  @beforeMethod({
    classNamePattern: /^Article/,
    methodNamePattern: /^(get|set)/
  })
  invokeBeforeMethod(meta: Metadata) {
    // meta.advisedMetadata == { bar: 42 }
    console.log(`Inside of the logger. Called ${meta.className}.${meta.method.name} with args: ${meta.method.args.join(', ')}.`);
  }
}

class Article {
  id: number;
  title: string;
  content: string;
}

@Advised({ bar: 42 })
class ArticleCollection {
  articles: Article[] = [];
  getArticle(id: number) {
    console.log(`Getting article with id: ${id}.`);
    return this.articles.filter(a => {
      return a.id === id;
    }).pop();
  }
  setArticle(article: Article) {
    console.log(`Setting article with id: ${article.id}.`);
    this.articles.push(article);
  }
}

new ArticleCollection().getArticle(1);

// Result:
// Inside of the logger. Called ArticleCollection.getArticle with args: 1.
// Getting article with id: 1.

In case you're using aspect.js in a browser environment the minifier may break the annotated code because of the performed mangling. In order to handle this problem you can use:

class LoggerAspect {
  @beforeMethod({
    classes: [ArticleCollection],
    methods: [ArticleCollection.prototype.getArticle, ArticleCollection.prototype.setArticle]
  })
  invokeBeforeMethod(meta: Metadata) {
    // meta.advisedMetadata == { bar: 42 }
    console.log(`Inside of the logger. Called ${meta.className}.${meta.method.name} with args: ${meta.method.args.join(', ')}.`);
  }
}

class ArticleCollection {
  getArticle(id: number) {...}
  setArticle(article: Article) {...}
}

In this case you can omit the @Advised decorator.

This way, by explicitly listing the classes and methods which should be woven, you can prevent the unwanted effect of mangling.

Demo

git clone https://github.com/mgechev/aop.js --depth 1
npm install -g ts-node
ts-node demo/index.ts

API

The library offers the following combinations of advices and join points:

Method calls

• beforeMethod(MethodSelector) - invoked before method call
• afterMethod(MethodSelector) - invoked after method call
• aroundMethod(MethodSelector) - invoked around method call
• onThrowOfMethod(MethodSelector) - invoked on throw of method call
• asyncOnThrowOfMethod(MethodSelector) - invoked on throw of async method call

Static method calls

• beforeStaticMethod(MethodSelector) - invoked before static method call
• afterStaticMethod(MethodSelector) - invoked after static method call
• aroundStaticMethod(MethodSelector) - invoked around static method call
• onThrowOfStaticMethod(MethodSelector) - invoked on throw of static method call
• asyncOnThrowOfStaticMethod(MethodSelector) - invoked on throw of async static method call

Accessors

• beforeSetter(PropertySelector) - invoked before setter call
• afterSetter(PropertySelector) - invoked after setter call
• aroundSetter(PropertySelector) - invoked around setter call
• onThrowOfSetter(PropertySelector) - invoked on throw of setter call
• asyncOnThrowOfSetter(PropertySelector) - invoked on throw of async setter call
• beforeGetter(PropertySelector) - invoked before getter call
• afterGetter(PropertySelector) - invoked after getter call
• aroundGetter(PropertySelector) - invoked around getter call
• onThrowOfGetter(PropertySelector) - invoked on throw of getter call
• asyncOnThrowOfGetter(PropertySelector) - invoked on throw of async getter call

MethodSelector

export interface MethodSelector {
  classNamePattern?: RegExp;
  methodNamePattern?: RegExp;
  classes?: Function[];
  methods?: Function[];
}

PropertySelector

export interface PropertySelector {
  classNamePattern?: RegExp;
  propertyNamePattern?: RegExp;
  classes?: Function[];
  properties?: PropertyDescriptor[];
}

Metadata

export class Metadata {
  public method: MethodMetadata;
  public className: string;
  public advisedMetadata: any;
}

MethodMetadata

export class MethodMetadata {
  public proceed: boolean;
  public name: string;
  public args: any[];
  public context: any;
  public result: any;
  public exception: any;
  public invoke: (...args: any[]) => any;
}

Diagram

Here's a UML class diagram which shows the relations between the individual abstractions:

Roadmap

• Tests
• Type annotations and DTS generation
• Aspect factories
  • Generic aspects
• Implement the following advices:
  • Before
  • After
    • Throwing
    • Returning
  • Around
• Implement the following join points:
  • Method execution
  • Static method execution
  • Filed get
  • Field set

License

MIT