ng-sugar

Syntactic sugar utils for Angular. This project was generated with Angular CLI version 10.0.3 (boilerplate is frightening though).

Installation

npm install --save ng-sugar

or

yarn add ng-sugar

Purpose

Reduce the boilerplate in rxjs-first workflows. Angular itself is not centered around rxjs yet it uses it to a degree, where at times logic starts looking convoluted and a bit boilerplaty when we start mixing observables with component lifecycle, Inputs, ViewChild, etc.

For example, let's say we want to make a component that can define its own navigation items and pass it back to parent component that manages the appshell's navigation bar. One way would be to write:

@Component({
    selector: 'hero-component',
    template: `
        <p>Hero Component</p>

        <ng-template #items>
            <button mat-icon-button>
                <mat-icon>arrow_drop_up</mat-icon>
            </button>
        </ng-template>
    `
})
export class HeroComponent {
    @ViewChild("items", {static: false}) items: TemplateRef<any>
    @Output() appbarItems = new EventEmitter<TemplateRef<any>>()

    ngAfterViewInit(): void { 
        this.appbarItems.emit(this.items)
    }
}

Doing this is totally fine as long as there no code that will run prior to ngAfterViewInit() that touches this.items which are undefined in that case.

As an alternative, we can utilize ObservableComponent that has lifecycle hooks as observables, then expessing our logic on top of this observable. Above will now look like:

import {ObservableComponent} from "ng-sugar";

//...
export class HeroComponent extends ObservableComponent {
    @ViewChild("items", {static: false}) items: TemplateRef<any>
    // emits once on afterViewInit
    items$ = this.afterViewInit.pipe(map(() => this.items))

    @Output() appbarItems = new EventEmitter<TemplateRef<any>>()

    constructor(){
        super()

        this.items$.subscribe(
            items => this.appbarItems.emit(items),
            console.error)
    }
}

About

This is a small set of utils that might be part of Angular core itself one day. It consists of

• ObservableComponent
• ngLet directive
• ObservableInput reimported from insidewhy/observable-input

ObservableComponent

Inheriting from ObservableComponent adds an observable counterpart to every lifecycle hook (with ng prefix removed). ngAfterViewInit in the below example is available as this.afterViewInit:

import {ObservableComponent} from "ng-sugar";

//...
export class HeroComponent extends ObservableComponent {
    @ViewChild("items", {static: false}) items: TemplateRef<any>
    // emits once on afterViewInit
    items$ = this.afterViewInit.pipe(map(() => this.items))
}

NgLet

We can unwrap an observable inside a template using *ngIf directive utilizing as binding, like:

<ng-container *ngIf="groupId$ | async as groupId">
</ng-container>

Before groupId$ emits or if it is null, above ng-container won't be rendered to the DOM. When it is not desired, replacing the above with *ngLet handles this usecase:

<ng-container *ngLet="groupId$ | async as groupId">
</ng-container>

ObservableInput

See insidewhy/observable-input

Contributing

Check CONTIBUTING.md

Attribution

This package is MIT, but it reimports ObservableInput from insidewhy/observable-input which doesn't include LICENSE, please ask in insidewhy/observable-input/issues for clarification.