@travetto/context

Async Context

Async-aware state management, maintaining context across asynchronous calls.

Install: @travetto/context

npm install @travetto/context

# or

yarn add @travetto/context

This module provides a wrapper around node's async_hooks to maintain context across async calls. This is generally used for retaining contextual user information at various levels of async flow.

The most common way of utilizing the context, is via the WithAsyncContext decorator. The decorator requires the class it's being used in, to have a AsyncContext member, as it is the source of the contextual information.

The decorator will load the context on invocation, and will keep the context active during the entire asynchronous call chain.

Code: Usage of context within a service

import { AsyncContext, WithAsyncContext } from '@travetto/context';

export class ContextAwareService {

  constructor(public context: AsyncContext) { }

  @WithAsyncContext()
  async complexOperator(name: string) {
    this.context.set({ name });
    await this.additionalOp('extra');
    await this.finalOp();
  }

  async additionalOp(additional: string) {
    const { name } = this.context.get();
    this.context.set({ name: `${name} ${additional}` });
  }

  async finalOp() {
    const { name } = this.context.get();
    // Use name
    return name;
  }
}

The decorator also allows for a priming of the contextual information. This is generally useful for system generated operations that are not initiated by a user.

Code: Usage of context within a service

import { AsyncContext, WithAsyncContext } from '@travetto/context';

export class SystemInitiatedContext {

  constructor(public context: AsyncContext) { }

  @WithAsyncContext({
    user: 'system',
    uid: 20
  })
  async runJob(name: string) {
    console.log('Running', { user: this.context.get().user, jobName: name });
  }
}