'Property does not exist on type 'never'

Ray_Booysen_42124 0
Viewed 396043

This is similar to #40796374 but that is around types, while I am using interfaces.

Given the code below:

interface Foo {
  name: string;
}

function go() {
  let instance: Foo | null = null;
  let mutator = () => {
   instance = {
     name: 'string'
   };  
  };

  mutator();

  if (instance == null) {
   console.log('Instance is null or undefined');
  } else {
   console.log(instance.name);
  }
}

I have an error saying 'Property 'name' does not exist on type 'never'.

I don't understand how instance could ever be a 'never'. Can anyone shed some light on this?

typescript
15 Answers

if you write Component as React.FC, and using useState(),

just write like this would be helpful:

const [arr, setArr] = useState<any[]>([])
user_123238370

I had the same error and replaced the dot notation with bracket notation to suppress it.

e.g.:

obj.name -> obj['name']
user_43716180

if you're receiving the error in parameter, so keep any or any[] type of input like below

getOptionLabel={(option: any) => option!.name}

 <Autocomplete
    options={tests}
    getOptionLabel={(option: any) => option!.name}
    ....
  />
user_81086840

In my own case when I was initiating the array. I used:

selectedActors: any = [];

So it makes it "dynamic" at first

user_110844430

For me the following code is working:

const [disc, setDisc] = useState<any[]>([]);

What I've seen this far is the following: When you don't specify the type you are passing to the useState() it inferes it is type never. By make it use the any[] you are able to pass the data when it is requested.

user_111101300

In your component.ts file just declare the array as the following

public arrayName = ([] as any[]);

that's worked with me for Angular

user_123505940

It happened to me when I forgot to define a type for the variable.

user_36315210

In my case (I'm using typescript) I was trying to simulate response with fake data where the data is assigned later on. My first attempt was with:

let response = {status: 200, data: []};

and later, on the assignment of the fake data it starts complaining that it is not assignable to type 'never[]'. Then I defined the response like follows and it accepted it..

let dataArr: MyClass[] = [];
let response = {status: 200, data: dataArr};

and assigning of the fake data:

response.data = fakeData;
user_75472750

in useState if u've never declared the type :

it assumes it is type is never so it shows this error :"Property does not exist on type 'never'"

you can type it as :

const [datalist, setDataList] = useState<Array<Object>>([]);
user_104621260

In my case it was happening because I had not typed a variable.

So I created the Search interface

export interface Search {
  term: string;
  ...
}

I changed that

searchList = [];

for that and it worked

searchList: Search[];
user_97355080

I was having problems with ? and !

This piece worked for me.

if (ref != null){
    if (ref.current != null)
        ref.current.appendChild(child);
}
user_101766650

I've came across the issue with the following expression:

const node = item ? <a href={item.link}>{item.name}</a> : item.name

And the else part item.name said Property 'name' does not exist on type 'never'.

Well this is because if there is nothing inside the item object - there can't be a name property as well.

So this warning happens when you declare something basically impossible (that's why it's never)

user_63550240

For typescript developer... if you use React.useRef() hook Instead of pre-assign null, declare and use variable type any.

Example:

const initialRef: any = null;
const ref = React.useRef(initialRef);
user_193488200
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