udemy.angular/docs/pipes.md

# Pipes

Pipes transform output in the template.

<img src="../img/pipes.png" alt="overview" width="300"/>

The Data remains the same as the output change.

The right place to place a pipe, is in the template.

Example of piping
```html
<li
class="list-group-item"
*ngFor="let server of servers | filter:filteredStatus:'status'"
[ngClass]="getStatusClasses(server)">
    <span
    class="badge">
    {{ server.status }}
    </span>
    <strong>{{ server.name | shorten:15 }}</strong> |
    {{ server.instanceType | uppercase }} |
    {{ server.started | date:'fullDate' | uppercase }}
</li>
```

Chaining the pipes together the order is important.

Angular pipe [documentation](https://angular.io/api?query=pipe)

## Create custom pipe

```ts
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'filter',
  pure: false
})
export class FilterPipe implements PipeTransform {

  transform(value: any, filterString: string, propName: string): any {
    if (value.length === 0 || filterString === '') {
      return value;
    }
    const resultArray = [];
    for (const item of value) {
      if (item[propName] === filterString) {
        resultArray.push(item);
      }
    }
    return resultArray;
  }

}
```

If Data are changed, the pipe dont get updated. For example if the application applies a filer pipe.