Angular map function is returning "undefined is not a function" - json

Question

I'm following this tutorial https://www.barbarianmeetscoding.com/blog/2016/04/02/getting-started-with-angular-2-step-by-step-6-consuming-real-data-with-http/, with Angular2 and VS Code.
I created a db.json server to test an api with, with the test data looking like
{
"articles": [{
"id": 1,
"name": "Wand of Lightning",
"description": "A powerful wand of ligthning.",
"price": 50,
"imageUrl": "/assets/images/wand.png",
"specs": [{
"name": "weight",
"value": 10
}, {
"name": "height",
"value": 22
}, {
"name": "material",
"value": "wood"
}],
"reviews": [{
"author": "Jaime",
"title": "I loved it!",
"content": "I loved the wand of ligthning! I usually use it to charge my laptop batteries!",
"rating": 5
}, {
"author": "John Doe",
"title": "Underwhelming",
"content": "I didn't like it at all...",
"rating": 1
}]
}, {
"id": 2,
"name": "Staff of Fire",
"description": "A powerful staff of fire.",
"price": 150,
"imageUrl": "/assets/images/staff-of-fire.png",
"specs": [{
"name": "weight",
"value": 10
}, {
"name": "height",
"value": 22
}, {
"name": "material",
"value": "wood and alabaster"
}],
"reviews": [{
"author": "Jaime",
"title": "I loved it!",
"content": "I loved the wand of ligthning! I usually use it to charge my laptop batteries!",
"rating": 5
}, {
"author": "John Doe",
"title": "Underwhelming",
"content": "I didn't like it at all...",
"rating": 1
}]
}
Now if I try to adapt my code to the sample, I get
undefined is not a function
Here's items.component.ts
import { Component, OnInit } from '#angular/core';
import {ItemsService} from '../items.service';
import {Item} from '../item';
#Component({
selector: 'app-items',
templateUrl: './items.component.html',
styleUrls: ['./items.component.css']
})
export class ItemsComponent implements OnInit {
items: Item[] = [];
errorMessage: string = '';
isLoading: boolean = true;
constructor(private itemsService: ItemsService) { }
ngOnInit() {
this.itemsService
.getAll().
subscribe(
p => this.items =p,
e => this.errorMessage = e,
/* onCompleted */ () => this.isLoading = false
)
}
}
items.service.ts
import { Injectable } from '#angular/core';
import { Http, Response, RequestOptions, Headers } from '#angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import 'rxjs/add/observable/throw';
import {Item} from './item';
#Injectable()
export class ItemsService {
private baseUrl: string ='http://localhost:3000';
constructor(private http: Http) {
}
getAll(): Observable<Item[]>{
let items = this.http
.get(`${this.baseUrl}/articles`, { headers: this.getHeaders()})
.map(this.mapItems)
.catch(this.handleError);
return items;
}
private getHeaders(){
let headers = new Headers();
headers.append('Accept', 'application/json');
return headers;
}
mapItems(response:Response): Item[]{
return response.json().map(this.toItem)
}
toItem(r:any): Item{
let result = <Item>({
id: r.id,
name: r.name,
description: r.description,
price: r.price,
imageUrl: r.imageUrl,
});
console.log('Parsed item:', result);
return result;
}
// this could also be a private method of the component class
handleError (error: any) {
// log error
// could be something more sofisticated
let errorMsg = error.message || `Yikes! There was a problem with our hyperdrive device and we couldn't retrieve your data!`
console.error(errorMsg);
// throw an application level error
return Observable.throw(errorMsg);
}
}
Note: making
return response.json().map(this.toItem)
Into
return response.json()
works. But I would like to get map working.
EDIT: Screenshot

Answer 1

this will solve your issue -
getAll(): Observable<Item[]> {
const items = this.http
.get(`${this.baseUrl}/articles`, {headers: this.getHeaders()})
.map((response: Response) => this.mapItems(response.json()))
.catch(this.handleError);
return items;
}
mapItems(data: Array<any>): Item[] {
return data.map(item => this.toItem(item));
}

Answer 2

I think what you want to map (Array.prototype.map) is the articles in your response object, and not the object itself. Do this:
mapItems(response:Response): Item[]{
return response.json().articles.map(this.toItem)
}