CODEWITHSUNDEEP
reactjstypescript
Álvaro
Álvaro

Reputation: 2588

Reduce on TypeScript

I am trying to run a reduce on an array of objects but TypeScript says:

`Argument of type 'string' is not assignable to parameter of type 'never'`

I know it defaults to never because I need to declare the array of strings but I do not know where should I do it here

store.ts

// I have this data on a context provider

const data = [{
  Name: 'Peter',
  Dept: 'Finance'
},{
  Name: 'Jane',
  Dept: 'HR'
},{
  Name: 'Tom',
  Dept: 'HR'
}]

import { useMainContext } from './store'

function App = () {

  const { data } = useMainContext()
  const [departments, setDepartments] = useState<string[] | undefined>([])


  type Props = {
    Name: string,
    Dept: string
  }

  // I dont now where to include the props

  useEffect(() => {
    const depts = data.reduce((acc, current) => {
     if (!acc.includes(current.Dept))
      acc.push(current.Dept)
     return acc
    }, [])

    setDepartments(depts)
  }, [])
...
}

Upvotes: 0

Views: 1165

Answers (1)

Rajiv Punjabi
Rajiv Punjabi

Reputation: 512

Just use Type Assertion for your initial value for .reduce()

const depts = data.reduce((acc, current) => {
 if (!acc.includes(current.Dept))
  acc.push(current.Dept)
 return acc
}, [] as string[]) //Added as string[]

Upvotes: 2

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