[Angular 2] implements OnInit, OnDestory for fetching data from server

Link: https://angular.io/docs/js/latest/api/core/OnInit-interface.html, https://www.youtube.com/watch?v=bY92HFyaBvo

export interface OnInit

exported from angular2/core defined in angular2/src/core/linker/interfaces.ts (line 79)

Implement this interface to execute custom initialization logic after your directive's data-bound properties have been initialized.

ngOnInit is called right after the directive's data-bound properties have been checked for the first time, and before any of its children have been checked. It is invoked only once when the directive is instantiated.

Keep it as a best pratices that implements OnInit, OnDestroy. Then inside ngOnInit, we call service to fetch data back. And in ngOnDestroy, we unsubscribe the Observable.

import {Component, ElementRef, EventEmitter, Output, OnInit, OnDestroy} from 'angular2/core';
import {Observable} from 'rxjs/Rx';
import {SearchServcie} from './SearchServcie';

@Component({
    selector: 'search-input',
    template: `<input type="text" autofocus>`
})

export class SearchInput implements OnInit, OnDestroy{

    @Output() loading = new EventEmitter();
    @Output() results = new EventEmitter();

    private _subscription;

    constructor(
        public youtube: SearchServcie,
        private el:ElementRef) {}

    ngOnDestroy() {
        // Unsubscribe the Observabler
        console.log('ngOnDestroy');
　　　　　if(this._subscription)　
            this._subscription.unsubscribe();
    }

    ngOnInit() {
        // Fetch the data from server
        console.log("init");
        const keyup$ = Observable.fromEvent(this.el.nativeElement, 'keyup');
        const searchInput$ = keyup$
            .debounceTime()
            .map((e:any) => {
                return e.target.value.trim();
            })
            .distinctUntilChanged()
            .filter((val:string) => {
                return val.length > ;
            })
            .do(() => {
                this.loading.emit(true);
            });
        const query$ = searchInput$
            .switchMap( (query) => this.youtube.doSearch(query));

        this._subscription = query$.subscribe((videos) => {
                this.results.emit(videos);
                this.loading.emit(false);
            }, (err) => {
                console.log(err);
                this.loading.emit(false);
            }, () => {
                this.loading.emit(false);
            });
    }
}