How can I get AsyncLocalStorage to work like ContextVar?

If you are working with TypeScript and trying to use AsyncLocalStorage in a similar way to ContextVar, you might have encountered some difficulties. In this blog post, we will explore different solutions to help you achieve the desired functionality.

Solution 1: Using Promises

One way to make AsyncLocalStorage work like ContextVar is by using Promises. You can create a helper function that wraps the AsyncLocalStorage methods and returns a Promise. This way, you can use async/await syntax to access the stored value.


import { AsyncLocalStorage } from 'async_hooks';

const asyncLocalStorage = new AsyncLocalStorage();

function getAsyncLocalStorageValue() {
  return new Promise((resolve) => {
    asyncLocalStorage.getStore()?.get('value', resolve);
  });
}

async function myFunction() {
  const value = await getAsyncLocalStorageValue();
  // Use the value here
}

asyncLocalStorage.run({ value: 'Hello, World!' }, myFunction);

Solution 2: Using Callbacks

If you prefer using callbacks instead of Promises, you can modify the helper function to accept a callback function as a parameter. The callback will be invoked with the stored value.


import { AsyncLocalStorage } from 'async_hooks';

const asyncLocalStorage = new AsyncLocalStorage();

function getAsyncLocalStorageValue(callback: (value: any) => void) {
  asyncLocalStorage.getStore()?.get('value', callback);
}

function myFunction() {
  getAsyncLocalStorageValue((value) => {
    // Use the value here
  });
}

asyncLocalStorage.run({ value: 'Hello, World!' }, myFunction);

Solution 3: Using a Custom Wrapper

If you find yourself using AsyncLocalStorage in multiple places and want a more convenient way to access the stored value, you can create a custom wrapper class. This class can provide getter and setter methods for accessing the value.


import { AsyncLocalStorage } from 'async_hooks';

const asyncLocalStorage = new AsyncLocalStorage();

class MyContext {
  static getValue() {
    return asyncLocalStorage.getStore()?.get('value');
  }
  
  static setValue(value: any) {
    asyncLocalStorage.getStore()?.set('value', value);
  }
}

function myFunction() {
  const value = MyContext.getValue();
  // Use the value here
}

asyncLocalStorage.run({ value: 'Hello, World!' }, myFunction);

With the above solutions, you should be able to use AsyncLocalStorage in a similar way to ContextVar. Choose the solution that suits your coding style and requirements best.

Remember to import the necessary modules and adapt the code snippets to your specific use case. Happy coding!

How can I get AsyncLocalStorage to work like ContextVar?