Typescript object key with index

Question

I wnat to declare key with index like

interface myType {
        delivery_name1: string;
        delivery_name2: string;
        delivery_name3: string; 
        delivery_name4: string; 
        delivery_name5: string;
        ...n(20)
   }

I tried

  type Index ="1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"  ...
    type delivery_name = `delivery_name${Index}`

interface myType {
    [key: delivery_name]:string;
}

But got error. An index signature parameter type cannot be a literal type or generic type. Consider using a mapped object type instead

How to solve it ?

Would this help you? https://stackoverflow.com/a/51659490/10100812 — Edwin, May 04 '22 at 06:33
@Edwin It is solved, if you want leave an answer I will check it! — MINJA KIM, May 04 '22 at 08:46

score 2 · Answer 1 · edited May 04 '22 at 12:52

2

To add to Edwins excellent answer, if you want to do this n times...

type MakeSeries<T extends number,R extends unknown[] = []> = T extends R['length'] 
? never
: [...R,unknown]['length'] | MakeSeries<T, [...R, unknown]>


type Index = MakeSeries<20> // <-- n times
type delivery_name = `delivery_name${Index}`

type myType = {
    [key in delivery_name]: string;
}
//**
type myType = {
delivery_name1: string;
delivery_name2: string;
delivery_name3: string;
delivery_name4: string;
delivery_name5: string;
delivery_name6: string;
delivery_name7: string;
... 12 more ...;
delivery_name20: string;
**//

}

TypeScript Playground

edited May 04 '22 at 12:52

Edwin

395
2
12

answered May 04 '22 at 09:59

Frallan

95
5

WOOOOW THNAKS!!! – MINJA KIM May 04 '22 at 11:18
That's really cool!~ – Edwin May 04 '22 at 12:12

score 0 · Accepted Answer · answered May 04 '22 at 08:55

You cannot use interface for the type in this case. Please use a type instead:

type Index ="1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
type delivery_name = `delivery_name${Index}`

type myType = {
    [key in delivery_name]: string;
}

TypeScript Playground

Reference

Typescript object key with index

2 Answers2