Property does not exist on type never

Question

This is similar to  40796374 but that is around types  while I am using interfaces   Given the code below    x000D   x000D  interface Foo   x000D    name  string  x000D    x000D   x000D  function go     x000D    let instance  Foo   null   null  x000D    let mutator        gt    x000D     instance     x000D       name   string  x000D          x000D       x000D   x000D    mutator    x000D   x000D    if  instance    null    x000D     console log  Instance is null or undefined    x000D      else   x000D     console log instance name   x000D      x000D    x000D   x000D   x000D    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   Thanks in advance

User · Answer

This seems to be similar to this issue  False  quot Property does not exist on type  never  quot  when changing value inside callback with strictNullChecks  which is closed as a duplicate of this issue  discussion   Trade-offs in Control Flow Analysis  That discussion is pretty long  if you can t find a good solution there you can try this  if  instance    null        console log  Instance is null or undefined      else       console log instance  name      ok now

User · Answer

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 · Answer

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 · Answer

I had the same error and replaced the dot notation with bracket notation to suppress it   e g   obj name -  obj  name

User · Answer

Because you are assigning instance to null  The compiler infers that it can never be anything other than null  So it assumes that the else block should never be executed so instance is typed as never in the else block   Now if you don t declare it as the literal value null  and get it by any other means  ex  let instance  Foo   null   getFoo      you will see that instance will be null inside the if block and Foo inside the else block   Never type documentation  https   www typescriptlang org docs handbook basic-types html never  Edit   The issue in the updated example is actually an open issue with the compiler   See   https   github com Microsoft TypeScript issues 11498 https   github com Microsoft TypeScript issues 12176

User · Answer

if you write Component as React FC  and using useState     just write like this would be helpful   const  arr  setArr    useState lt any   gt

User · Answer

if you re receiving the error in parameter  so keep any or any   type of input like below getOptionLabel   option  any    gt  option  name     lt Autocomplete     options  tests      getOptionLabel   option  any    gt  option  name               gt

[typescript] 'Property does not exist on type 'never'

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