TypeScript type for initial empty object

Question

I am having problems with TypeScript on this code which works well on normal JS

I get this error form TypeScript:

`Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{}'`

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

const groups = {}
for (const { Name, Department } of data) {
  if (!groups[Department]) groups[Department] = { title: Department, people: [] }
  groups[Department].people.push(Name)
}
console.log(Object.values(groups))

.as-console-wrapper { max-height: 100% !important; top: 0; }

I have tried to add the Props

type Props = {
  title?: string
  people?: string[]
}

const groups: Props | undefined = {}

But I still get a similar error

`Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'Props'.`

groups: { [key: string]: { title: string, people: string[] } } = {}; typescriptlang.org/play?#code/… — Jared Smith
– Jared Smith, Commented Mar 16, 2021 at 16:06
Thanks it also worked with const groups: { [key: string]: Props } = {} — Álvaro
– Álvaro, Commented Mar 16, 2021 at 16:10
There is a utility type Record<Keys, Values> which is a shorthand for the “[key: string]:” index. You can use Record<string, Props> if that’s more readable. Functionally it’s the same. It means an object whose keys are type string and whose values are type Props. Also I would make the properties on Props required rather than optional. — Linda Paiste
– Linda Paiste, Commented Mar 16, 2021 at 17:11

Ben Wainwright · Accepted Answer · 2021-03-16 16:08:32Z

2

Try this:

type Department = { [name: string]: { title: string; people: string[] } };

const groups: Department = {};

answered Mar 16, 2021 at 16:08

Ben Wainwright

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