find（）不返回数据，仅未定义

Question

I want to find() s_id form this JSON:

 {
        "StatusCode": 0,
        "StatusMessage": "OK",
        "StatusDescription": [
             {
                "s_id": "11E8C70C8A5D78888E6EFA163EBBBC1D",
                "s_serial": "PkMGo",
                "active": 0,
              },
             {
                "s_id": "11E8C70FB9D10DB38E6EFA163EBBBC1D",
                "s_serial": "UgooX",
                "active": 0,
                },
              {
                "s_id": "11E8C7179F85836D8E6EFA163EBBBC1D",
                "s_serial": "IiLnM",
                "active": 0,
                }, .....
            {
                "s_id": "11E8C71905123F1A8E6EFA163EBBBC1D",
                "s_serial": "LVpcP",
                "active": 0,
             }
              }]}

I try to find in this but return undefined.

 sensors: Sensors[]=[];
 hbp: HBP;
 sensor: Sensors;

     this.ss.getAllS().subscribe(
          sensors => {
            this.sensors = sensors 
            let ss = this.sensors.find(x => x.s_id ===  this.hbp.s_id);
            console.log(ss)
            if (ss) {
              this.selectedSensor = ss.s_id
            }
          }
        );

and

 selectedSensor : string = this.sensors.filter(
    x => x.s_id === this.sensor.s_id[0])
    .map(y => y.s_serial).join('');

I think that I have problem in this line:

        let ss = this.sensors.find(x => x.s_id ===  this.hbp.s_id);

because, hbp return this json:

active: 0
homebox_id: "11E8C71154CC8C188E6EFA163EBBBC1D"
sensors: Array(2)
0: {s_serial: "s_id", s_id: "11E8C70C8A5D78888E6EFA163EBBBC1D"}
1: {s_serial: "UgooX", s_id: "11E8C70FB9D10DB38E6EFA163EBBBC1D"}

and in this line maybe will find inside this sensors

This selectedSensor I used in html code

<input formControlName="s_id" type="text" placeholder="Select " [(ngModel)]="selectedSensor" aria-label="Number" matInput
            [matAutocomplete]="auto">

How to return data ?

Can you ask me any idea please?

Answer 1

Use can use find function like below

  let ss =   this.sensors.find((item) => {
      return item.s_id === this.hbp.s_idl
    })


if (ss) {
    this.selectedSensor = ss.s_id         
      }

If you are looking for filter,map and join combination , Please make sure you are returning the item.property inside map

.filter((item) => {
  return item.s_id ===  ss.s_id
}).map(
  (item) => {
    return item.s_serial
  }
).join( )

Check this sample code

https://stackblitz.com/edit/arrayfind?file=index.js

Answer 2

Your code seems fine to me, are you sure that this.ss.getAllS() method returns an array of StatusDescription types? I would recommend to debug what is actually in sensors variable at runtime.

Answer 3

The observable: sensors, will initially be null, and you can't access properties of null to compare anything to.

Instead, do a quick null check on the sensors value, then do your find operation:

this.ss.getAllS().subscribe(sensors => {
  if (sensors) {
    this.selectedSensor = this.sensors.find(x => x.s_id === this.hbp.s_id)
  }
});

Here's a StackBlitz example: https://stackblitz.com/edit/select-id-from-observable