observable-input's Introduction

Installation

npm install -S observable-input

yarn add observable-input

Usage

import { Component, Input } from '@angular/core'
import { Observable } from 'rxjs/Observable'
import { ObservableInput } from 'observable-input'

@Component({
  templateUrl: './some-component.html',
  selector: 'app-some-component',
})
class SomeComponent {
  @Input() @ObservableInput()
  private index: Observable<number>

  @select()
  private selectedIndex: Observable<number>

  public isSelected = this.index.switchMap(
    index => this.selectedIndex.map(selectedIndex => selectedIndex === index)
  )
}

Then in some-component.html:

<span [class.selected]="isSelected | async">maybe selected</span>

Details

This decorator works by replacing the input with a property, the getter returns a value with type Observable<T> while the setter expects a variable of type T. This introduces a few drawbacks:

While you should generally only be reading your input values and not setting them, the mismatch of types for the setter and getter here is still potentially a source of confusion.
For now the angular code (whether AOT compiled or not) only writes to a component's inputs (in this case via the setter) and never reads from them, if it did it would receive a value with type Observable<T> when it expects a value of type T.
The angular compiler does not type check the values passed to a component match the types of the @Input, if it did it would raise an error indicating that the input should be of type Observable<T> instead of T.

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