Javascript - Element implicitly has an 'any' type. No index signature with a parameter of type 'string' was found on type 'User1'

ArunMuralidharan
April 6, 2024
229 views
0 votes
2 Answers

I tried using computed properties in typescript. But getting below error.

The checkParameter is random & will be decided on runtime.

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'User1'.
  No index signature with a parameter of type 'string' was found on type 'User1'

Code

type User1 = {
  name: string;
  age: number;
  address: string;
};

const user1: User1 = {
  name: "user1",
  age: 23,
  address: "address",
};

let checkParameter: string | number = "name";
console.log(user1[checkParameter]); //error occuring here

checkParameter = "age";
console.log(user1[checkParameter]); //error occuring here

checkParameter = "address";
console.log(user1[checkParameter]); //error occuring here

Im expecting, Error free execution.

Answers

- Santiago
- April 6, 2024 at 6:37 pm
- 0 votes
0
You can add [key: string]: string to specify that the type User1 has properties with keys of type string
```
type User1  = {
   [key: string]: any;
   name: string;
   age: number;
   address: string;
};

const user1: User1 = {
   name: "user1",
   age: 23,
   address: "address",
};

let checkParameter: string | number = "name";
console.log(user1[checkParameter]);
```
Since checkParameter has two types string | number and it refers to a key, if the User1 type will have a key of type number, add this type to the key:
```
type User1  = {
   [key: string | number]: any
   name: string;
   age: number;
   address: string;
};
```
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- uncle_baby_kern
- April 6, 2024 at 10:43 pm
- 0 votes
0
One solution is to change the type for checkParameter to a union of the strings representing each property.
let checkParameter: name" | "age" | "address" = "name"

Update: As @jcalz suggested, keyof User1 would dynamically represent the User1 properties:
```
type User1 = {
  name: string;
  age: number;
  address: string;
};

const user1: User1 = {
  name: "User 1",
  age: 23,
  address: "123 First St",
};

let checkParameter: keyof User1 = "name";
console.log(user1[checkParameter]); // User 1

checkParameter = "age";
console.log(user1[checkParameter]); // 23

checkParameter = "address";
console.log(user1[checkParameter]); // 123 First St
```
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