Angular 4: How to watch an object for changes?

Question

ETA: I know that there are various ways to watch my form for changes. That is not what I am trying to do. As the title says, I am asking how to watch for change

Answer 1

You could use custom setters to trigger your callback:

class Customer {
  private _firstName: string
  get firstName(): string {
    return this._firstName
  }
  set firstName(firstName: string) {
    this.valueChanged(this._firstName, firstName)
    this._firstName = firstName
  }

  private _lastName: string
  get lastName(): string {
    return this._lastName
  }
  set lastName(lastName: string) {
    this.valueChanged(this._lastName, lastName)
    this._lastName = lastName
  }

  valueChanged: (oldVal, newVal) => void

  constructor (valueChanged?: (oldVal, newVal) => void) {
    // return an empty function if no callback was provided in case you don't need
    // one or want to assign it later
    this.valueChanged = valueChanged || (() => {})
  }
}

Then just assign the callback when you create the object:

this.customer = new Customer((oldVal, newVal) => console.log(oldVal, newVal))

// or

this.customer = new Customer()
this.customer.valueChanged = (oldVal, newVal) => console.log(oldVal, newVal)