How to apply filters to *ngFor?

Question

Apparently, Angular 2 will use pipes instead of filters as in Angular1 in conjunction with ng-for to filter results, although the implementation still seems to be vague, with no clear documentation.

Namely what I'm trying to achieve could be viewed from the following perspective

<div *ng-for="#item of itemsList" *ng-if="conditon(item)"></div>

How to implement so using pipes?

Answer 1

Basically, you write a pipe which you can then use in the *ngFor directive.

In your component:

filterargs = {title: 'hello'};
items = [{title: 'hello world'}, {title: 'hello kitty'}, {title: 'foo bar'}];

In your template, you can pass string, number or object to your pipe to use to filter on:

<li *ngFor="let item of items | myfilter:filterargs">

In your pipe:

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

@Pipe({
    name: 'myfilter',
    pure: false
})
export class MyFilterPipe implements PipeTransform {
    transform(items: any[], filter: Object): any {
        if (!items || !filter) {
            return items;
        }
        // filter items array, items which match and return true will be
        // kept, false will be filtered out
        return items.filter(item => item.title.indexOf(filter.title) !== -1);
    }
}

Remember to register your pipe in app.module.ts; you no longer need to register the pipes in your @Component

import { MyFilterPipe } from './shared/pipes/my-filter.pipe';

@NgModule({
    imports: [
        ..
    ],
    declarations: [
        MyFilterPipe,
    ],
    providers: [
        ..
    ],
    bootstrap: [AppComponent]
})
export class AppModule { }

Here's a Plunker which demos the use of a custom filter pipe and the built-in slice pipe to limit results.

Please note (as several commentators have pointed out) that there is a reason why there are no built-in filter pipes in Angular.