---
name: angular-directives-pipes-108535d6e293
description: Build custom Angular attribute directives, HostDirectives, and pure pipes. Use for Angular directive or pipe implementation, including custom attribute directives; defer React/CSS middleware and unrelated framework work.
metadata:
  triggers:
    files:
      - "**/*.directive.ts"
      - "**/*.pipe.ts"
    keywords:
      - hostDirectives
      - PipeTransform
      - pure
---

# Directives & Pipes

## **Priority: P2 (MEDIUM)**

## Principles

- **Composition**: Use **hostDirectives: [TooltipDirective]** on `@Component` or `@Directive` decorators to compose behaviors without inheritance. Expose inputs/outputs via **hostDirectives: [{ directive: TooltipDirective, inputs: ['text'] }]**.
- **Pure Pipes**: Decorate with `@Pipe({ name: 'truncate', standalone: true, pure: true })`. Implement **PipeTransform** with `transform(value: string, limit = 50)` method. Pipes must **pure: true** (default) to **cache results** by input reference — Angular only re-runs them when reference changes. ** not set pure: false** unless handling Observables/Arrays that mutate.
- **Directive Logic**: Encapsulate reusable DOM manipulation or behavioral logic in **standalone: true** Directives (e.g., **selector: '[appHighlight]'**). **Inject ElementRef/Renderer2 for DOM access**.

## Guidelines

- **Signal Inputs**: Directives and Pipes support signal inputs.
- **Standalone**: All Pipes and Directives must standalone. ** not declare in NgModule**; import directly in component **imports array**. Use **ng generate directive** to scaffold.

## Anti-Patterns

- **No @HostBinding/@HostListener**: Use **host: {} object** in `@Directive` decorator — not with @HostBinding or @HostListener (e.g., **'(mouseenter)': 'show()'**, **'[attr.aria-label]': 'text()'**) — these decorators deprecated patterns.
- **No impure pipes for static transforms**: Keep `pure: true` (default); use `async` pipe for Observables.
- **No structural directives for conditionals**: Use native `@if`/`@for`/`@switch` block syntax.

## References

- [Composition](references/composition.md)

## Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

- cache results
- host: {} object
- imports array
- not set pure: false
- not with @HostBinding


---
Source attribution: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Dave AI.

## Upstream license notice

MIT License

Copyright (c) 2026 Gabriel Moreira

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Dave AI resource metadata

Creator / publisher: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
Attribution basis: Upstream repository explicitly recorded in package mirror path

Fields of work: Development & Engineering
Roles: Frontend Developer, Full-Stack Developer
Specialties: Cross Platform, Frontend
Tools: Angular
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 35393df35b37335805b449d41ace2303c67d241586c081d14690134ba0730bcf