@DependsOn

Overview

The @DependsOn decorator establishes reactive dependencies between getters of a class that extends PubSub or PubSubMixin.
When one or more dependent properties are updated and notified, all computed properties that depend on them are automatically notified as well.

This makes it possible to define reactive relationships declaratively within the class, improving consistency and reducing boilerplate code.

Example

Let's say you have a derived attribute based on the values of other attributes, and calculated via a get method, for example:

export class Person extends PubSub {
  constructor(public firstName: string, public lastName: string) {
    super();
  }

  @Notifies("firstName")
  public setFirstName(firstName: string) {
    this.firstName = firstName;
  }

  @Notifies("lastName")
  public setLastName(lastName: string) {
    this.lastName = lastName;
  }

  // fullName is a derived value of firstName and lastName
  public get fullName() {
    return [this.firstName, this.lastName].join(" ")
  }
}

In this case, you don't want to add fullName to the Notifies decorators of setFirstName and setLastName. It would work, of course, but it's repetitive and it requires setFirstName and setLastName to know what are the derived values that depend upon them. This is conceptually wrong: it's a responsibility of the derived value to know on what base values it depends on, not vice versa.

So in these cases, just use the DependsOn decorator:

export class Person extends PubSub {
  // ...

  @DependsOn("firstName", "lastName")
  public get fullName() {
    return [this.firstName, this.lastName].join(" ")
  }
}

By doing so, whenever firstName or lastName will be notified, also fullName will be notified.

Properties

Property	Type	Description
dependencies	(keyof TClass)[]	The list of class properties or getters this property depends on.

Notes

• Works only on classes extending or mixing in PubSub.
• Dependency tracking is stored in a shared WeakMap to avoid memory leaks.
• Circular dependencies must be avoided, as they can cause infinite notification loops.