Usage

Angular Primitives are built entirely using Angular directives, offering a flexible and composable way to enhance your components.

There are two main ways to use them:

• Apply the directives directly in your component templates.
• Use the directives as host directives in your own components.

Let’s explore both approaches, along with some limitations and the solutions we provide.

---

Using Directives in Templates

To use a directive in a template, simply apply it to the element you want to enhance. For example, here’s how you might use the ngpSwitch directive:

<button
  ngpSwitch
  [ngpSwitchChecked]="isChecked()"
  (ngpSwitchCheckedChange)="onSwitchChange($event)"
>
  <span ngpSwitchThumb></span>
</button>

This applies the ngpSwitch directive to the button, enabling correct behavior and accessibility. You have full control over the inputs and outputs, making this approach ideal for many use cases.

However, this method has a few limitations. Some directives — like ngpButton — are intended to be used on specific elements (e.g. button). Wrapping such elements in your own component can make it difficult for consumers to add attributes like type, since you'd need to expose every possible attribute as an input manually.

To solve this, you can use host directives.

Using Directives as Host Directives

Host directives let you enhance your components by attaching existing directives at the class level. Here's how you can use ngpButton as a host directive:

import { Component } from '@angular/core';
import { NgpButton } from 'ng-primitives/button';

@Component({
  selector: 'button[my-button]',
  template: `
    <ng-content />
  `,
  hostDirectives: [NgpButton],
})
export class MyButtonComponent {
  // You can add any additional inputs or outputs you want here
}

This approach allows consumers to apply attributes directly to the button element while still benefiting from the functionality provided by the directive.

You can also expose specific inputs and outputs from the directive to your component. For example:

import { Component, Input } from '@angular/core';
import { NgpButton } from 'ng-primitives/button';

@Component({
  selector: 'button[my-button]',
  template: `
    <ng-content />
  `,
  hostDirectives: [{ directive: NgpButton, inputs: ['disabled'] }],
})
export class MyButtonComponent {}

This lets consumers bind to the disabled input just as if they were using ngpButton directly.

Limitations & Solutions

Programmatically setting inputs

A key limitation of host directives in Angular is that their inputs can't be set programmatically within the component. To address this, we provide two main solutions:

Config Providers

Some directives support configuration providers that let you set default values. For example, to configure the default expansion type for ngpAccordion:

@Component({
  selector: 'my-accordion',
  template: `
    <ng-content />
  `,
  hostDirectives: [{ directive: NgpAccordion, inputs: ['type'] }],
  providers: [provideAccordionConfig({ type: 'multiple' })],
})
export class MyAccordionComponent {}

Consumers can still override this default by explicitly binding to the type input.

State Providers

Other directives provide a state provider, allowing you to programmatically control their inputs. For example:

import { Component } from '@angular/core';
import { NgpSwitch, injectSwitchState } from 'ng-primitives/switch';

@Component({
  selector: 'my-switch',
  template: `
    <ng-content />
  `,
  hostDirectives: [NgpSwitch],
})
export class MySwitchComponent {
  private readonly state = injectSwitchState();

  constructor() {
    this.state.checked.set(true);
  }
}

Internally, all directive inputs are converted into linked signals, enabling both binding and programmatic updates.

Splitting into Multiple Components

Some features are best implemented as multiple components. Take an accordion, for example:

<my-accordion>
  <my-accordion-item label="Item 1">
    <p>Content for item 1</p>
  </my-accordion-item>

  <my-accordion-item label="Item 2">
    <p>Content for item 2</p>
  </my-accordion-item>
</my-accordion>

If you're using ngpAccordion as a directive in the my-accordion template, the child my-accordion-item components won’t be able to locate it in the dependency injection tree. This is a known Angular limitation.

To solve this, Angular Primitives supports state hoisting, which allows you to share directive state between components.

State Hoisting Example

To hoist the state of ngpAccordion from the my-accordion component:

import { Component } from '@angular/core';
import { NgpAccordion, provideAccordionState } from 'ng-primitives/accordion';

@Component({
  selector: 'my-accordion',
  template: `
    <div ngpAccordion>
      <ng-content />
    </div>
  `,
  providers: [provideAccordionState()],
})
export class MyAccordionComponent {}

Now, child directives like ngpAccordionItem can correctly locate and interact with the hoisted ngpAccordion state.