Angular Signal Effect inside our outside Constructor

Does Angular have any guidance where I should put the Effect code? Is it generally inside Constructor or outside? What are the advantages / disadvantages for each method?

export class CustomerForm {
  lastName= input.required<string>();    

  constructor() {
    effect(() => {
      console.log('lastName changed:', this.lastName());
    });
  }
}

Solution

Where it can be

As per the documentation, by default, you can only create an effect() within an injection context:

During construction (via the constructor) of a class being instantiated by the DI system, such as an @Injectable or @Component.
In the initializer for fields of such classes.
In the factory function specified for useFactory of a Provider or an @Injectable.
In the factory function specified for an InjectionToken.
Within a stack frame that runs in an injection context.

But if you need to create an effect() outside of the constructor, you can pass an Injector via its options:

effect(() => {
  console.log(`The count is: ${this.count()}`);
}, {injector: this.injector});

Where it should be

If we look at how effect() has been implemented so far (July 2025) in the official Angular Material components, we find out that it's systematically called in the constructor or a private method called by the constructor.

It is the commonly accepted place for effects. That pattern should be followed to increase your code readability, unless there's a good reason not to.