typescript error: Object is possibly 'undefined'. when sorting array based on the contents of object map

Question

the error is currEmot is possibly undefined. I'm confused why that is occurring because the for loop is guaranteed to loop through the emotionsObject and add objects to the map.

let emotionsObject = [
{
    size: 80,
    background: 'rgb(67, 0, 128)',
    width: .5,
    emoji: "😄",
    name: 'joy'
},
{
    size: 34,
    background: 'rgb(0, 45, 172)',
    width: .35,
    emoji: "😭",
    name: 'sadness',
},
{
    size: 50,
    background: 'rgb(172, 6, 0)',
    width: .15,
    emoji: "😡",
    name: 'anger',
},
];
type T_Emotion = typeof emotionsObject[0] 
let currEmot = new Map<string, T_Emotion>(null!);
let emotOrder: string[] = [];
for (let i = 0; i < emotionsObject.length; i++) {
   let id = uuid_v4();
   emotOrder.push(id)
   currEmot.set(id, emotionsObject[I]);
}

emotOrder.sort((a: string, b: string):number => currEmot.get(b).width - currEmot.get(a).width);

I have tried these other versions to prevent this error.

emotOrder.sort((a: string, b: string):number => currEmot?.get(b)?.width - currEmot?.get(a)?.width);
emotOrder.sort((a: string, b: string):number => currEmot.get(b).width as number - currEmot.get(a).width as number);

null! ...huh?

CertainPerformance
– CertainPerformance

2021-11-11 01:05:22 +00:00
Commented Nov 11, 2021 at 1:05 — CertainPerformance
– CertainPerformance, Commented Nov 11, 2021 at 1:05
Where does the I come from all of the sudden?

Robby Cornelissen
– Robby Cornelissen

2021-11-11 01:07:58 +00:00
Commented Nov 11, 2021 at 1:07 — Robby Cornelissen
– Robby Cornelissen, Commented Nov 11, 2021 at 1:07

Andrei · Accepted Answer · 2021-11-11 01:12:28Z

2

use bang operator ! to tell typescript that there will be no situation where object is not found

currEmot.get(b)!.width - currEmot.get(a)!.width

answered Nov 11, 2021 at 1:12

Andrei

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3 Comments

glushkina1 Over a year ago

this operator gives another warning ESLint: Forbidden non-null assertion. (@typescript-eslint/no-non-null-assertion)

Andrei Over a year ago

you could use ?. operator instead, but I believe turning on "non-null assertion" rule in eslint is not right

glushkina1 Over a year ago

?. operator gives TS2532: Object is possibly 'undefined'. This answer helped stackoverflow.com/questions/65942654/…

glushkina1 · Accepted Answer · 2023-02-05 03:51:24Z

1

You need to creact Interface and set it to your object

interface IEmotions {
  size: number
  background: string
  width: number
  emoji: string
  name: string
}

Please keep in mind if any key could be undefined, you need to add ? to your key , for example: size?: number

let emotionsObject: (IEmotions | undefined)[] = [
 {
    size: 80,
    background: 'rgb(67, 0, 128)',
    width: .5,
    emoji: "😄",
    name: 'joy'
 }, 
 {
    size: 34,
    background: 'rgb(0, 45, 172)',
    width: .35,
    emoji: "😭",
    name: 'sadness',
 }
];

edited Feb 5, 2023 at 3:51

answered Feb 4, 2023 at 5:18

glushkina1

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