filter wont filter undefined-CodePudding

been staring at this code for while now..

Need some help

I have this filter, and im trying to remove undefined objects from array:

  .then((items) => {
    const filtered = items.map( i => {
      if (i !== undefined) {
        return i
      }
    })
    updateState(filtered, query)
  });

Followed by the filtered giving error:

Argument of type '({ service: Service; results: Card[]; } | undefined)[]' is not assignable to parameter of type 'SearchResult[]'.
  Type '{ service: Service; results: Card[]; } | undefined' is not assignable to type 'SearchResult'.
    Type 'undefined' is not assignable to type 'SearchResult'.

when i try to pass it to updateState() function.

Shouldn't the filter do just that? remove the undefined items from the array.. What is going on here?

EDIT: Even filtering with type assertion gives the same error..

const filtered: SearchResult[] = results.filter( i => i as SearchResult)

With same result..

Thanks

CodePudding user response：

If you do not return a value from the map function, it returns undefined, so the return from your current code for an undefined value is still undefined.

You can get your desired result by using filter instead of map, or by returning a default value other than undefined when your map encounters undefined.

CodePudding user response：

So, it turns out Typescript is not able to figure the type of return here..

after long while abusing google searches with different keywords i came up with this line

const filtered: SearchResult[] = results.filter( (i): i is SearchResult => !!i)

I got it from this blog post: https://www.benmvp.com/blog/filtering-undefined-elements-from-array-typescript/

Have a nice day everyone!