Tokens

In TypeDI, tokens can be used to create a reference to a static value inside the container. They can then be injected into services as regular dependencies.

As an example, let's update our Hello World! example to print the value of a token instead of a hard-coded string.

Creating our Token

First, we'll create a file which holds the token.

import { Token } from '@freshgum/typedi';

export const MESSAGE = new Token<string>('The message to print to the console.');

In TypeDI, tokens are created by making new instances of the Token class. It also accepts a type parameter, which sets the type of the value the token points to. Finally, a message is also accepted, which is used for debugging purposes within TypeDI.

tip

As with services, it's good practice to name your files according to what they contain. As this file centres around exporting a token, we add a ".token.ts" suffix to the file name.

Consuming our Token

Let's now update our logging service to print the value of the token.

import { Service } from '@freshgum/typedi';
import { MESSAGE } from './message.token';

@Service([MESSAGE])
export class LogService {
  constructor(private message: string) {}

  public log() {
    console.log(this.message);
  }
}

What we've done is update our LogService to consume the newly-created token as a dependency. Before we've created our container, TypeDI doesn't know what the value of the token is.

Setting the value of a Token

We'll now need to tell TypeDI what the value of MESSAGE should be before we create our LogService.

note

For brevity, the RootService service in the example is skipped here.

src/main.ts

import { Container } from '@freshgum/typedi';
import { LogService } from './log.service';
import { MESSAGE } from './message.token';

Container.set({ id: MESSAGE, value: 'Hello World!', dependencies: [] });

Container.get(LogService).log();

If we now run our code, we'll see the following:

$ ts-node ./src/main.ts
Hello World!

Did you know...

In TypeDI, tokens aren't treated specially. In fact, the implementation of Token is quite literally:

export class Token<T> {
  constructor(public name?: string) {}
}