How to update dependency injection token value

If you don't want to use a BehaviorSubject, you could provide a simple class with a getter and setter instead.

class MyValue {

  get value(): string {
    return this._value;   
  }

  set value(val: string) {
   this._value = val;
  }
  private _value = '';

}

const MY_VALUE_TOKEN = new InjectionToken<MyValue>('MY_VALUE_TOKEN ');

// Provide class in either module or component providers array.
providers: [
  { provide: MY_VALUE_TOKEN , useClass: MyValue },
]

class MyComponent {

  // Inject in component constructor
  constructor(
    @Inject(MY_VALUE_TOKEN) private _myValue: MyValue,
  ) {

    // Access current value
    console.log(this._myValue.value);

    // Set new value
    this._myValue.value = 'new value';
  }

}

Instead of a primitive which is immutable, you can use a BehaviorSubject, then access and update it in one component and subscribe in the other:

providers: [{ provide: MyValueToken, useValue: new BehaviorSubject('')}]

// consumer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.subscribe((my_value)=>this.title = my_value);
}

// producer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.next('my title value');
}

In addition to the Wizard:

If you have a use-case where every consumer needs its own instance of BehaviourSubject. (I happen to be in this use-case). Make sure you define a factory.

const myFactory = () => { return new BehaviorSubject<string>('') };

providers: [
    { provide: MyValueToken, useFactory: myFactory }
]

// Then, as proposed in the top-answer.

// consumer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.subscribe((my_value)=>this.title = my_value);
}

// producer
constructor(@Inject(MyValueToken) my_value: BehaviorSubject) {
  my_value.next('my title value');
}