use Angular6 Service constructor to initialize private attribute

Question

I'm trying to initialize a few objects in a Angular6 Service but I'm getting an error explaining that one of my private attribute is undefined.

At first I tried that :

private mockIncident: Incident[];

constructor() {
    this.mockIncidentRaw.forEach(incident => {
      this.mockIncident.push(new Incident().deserialize(incident))
    });
  }

But i got the error telling that mockIncident is not defined.
ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'push' of undefined.

And then tried that :

public mockIncident: Incident[];

  constructor() {
    init();
  }
  
  init = () => {
    for(let i = 0; this.mockIncidentRaw.length; i++) {
      this.mockIncident.push(new Incident().deserialize(this.mockIncidentRaw[i]))
    } 
  }

You never give it a value, just a type, so why is that surprising? — jonrsharpe, Feb 28 '20 at 13:58
Moreover, how is initialized `this.mockIncidentRaw`? I guess your problem are not over just with my response. — Axiome, Feb 28 '20 at 14:04
@jonrsharpe this.mockIncidentRaw contain the value, but not relevant here — NeitoFR, Feb 28 '20 at 14:07
@Exomus the only problem was that the array wasn't initialized as you mention in the second part of your answer — NeitoFR, Feb 28 '20 at 14:08
You're right, that's not relevant, that's not what you're trying to *push* to. — jonrsharpe, Feb 28 '20 at 14:08

Axiome · Accepted Answer · 2020-02-28T14:08:12.787

3

public mockIncident: Incident[]; is declaring an undefined object.

Do this public mockIncident: Incident[] = [] so there is an array initialization. Here you will have all the property of an array like push()

edited Feb 28 '20 at 14:08

answered Feb 28 '20 at 14:01

Axiome

695
5
18

For info ngOnInit doesn't work on services : "Lifecycle hooks, like OnInit() work with Directives and Components. They do not work with other types, like a service in your case." [link](https://stackoverflow.com/a/35110798/9243790), but the problem was that I didn't init the array to [], thanks – NeitoFR Feb 28 '20 at 14:06
My bad, I read wrongly your post on the type of angular component you are declaring. I'm updating my response, to correct my answer that was very misleading. I apologize – Axiome Feb 28 '20 at 14:07

score 2 · Answer 2 · answered Feb 28 '20 at 14:04

2

mockIncident array is not initialized, add = [];

private mockIncident: Incident[] = [];

answered Feb 28 '20 at 14:04

porgo

1,729
2
17
26

use Angular6 Service constructor to initialize private attribute

2 Answers2