No index signature with a parameter of type 'string' was found on type '

Question

I was working on my first firebase typescript function project

I have following code snippet.

const files = {
    status: './src/api/status.f.js',
    invite: './src/api/invite.f.js',
    user: './src/api/user.f.js',
    auth: './src/api/auth.f.js',
    social: './src/api/social.f.js'
}

for (let file in files)
    if (files.hasOwnProperty(file)) {
        // Setting function name equivalent to the file name
        if (!process.env.FUNCTION_NAME || process.env.FUNCTION_NAME === file) {
            const ApiClass = require(files[file])
            const app = new ApiClass(context)
            exports[file] = app.handler
        }
    }

In this, at this line i am getting following error const ApiClass = require(files[file])

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type '{ status: string; invite: string; user: string; auth: string; social: string; }'. No index signature with a parameter of type 'string' was found on type '{ status: string; invite: string; user: string; auth: string; social: string; }'

Primary Question: Can someone help me figure out what I am doing wrong here?

hackape · Accepted Answer · 2020-09-29 17:13:36Z

18

The type error is shown because you turned on "noImplicitAny": true in tsconfig.

If you like to keep "noImplicitAny": true, then there're 2 fixes to your problem, choose either one.

const ApiClass = require(files[file as keyof typeof files])
const files: { [key: string]: string } = { ... }

After some digging, I think the optimal way is to augment the Object.prototype.hasOwnProperty() method's signature.

// somewhere in your project, write:

interface Object {
  hasOwnProperty<T>(this: T, v: any): v is keyof T
}

This way .hasOwnProperty acts as a type guard that narrows down type of file to be keyof typeof files automatically.

edited Sep 29, 2020 at 17:13

answered Nov 12, 2019 at 4:59

hackape

20.3k2 gold badges34 silver badges72 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Malik Alimoekhamedov Over a year ago

There's another cool way of typing objects in TypeScript, by the way: const myObj: Record<string, number | RegExp> = {...};

gmustudent · Accepted Answer · 2024-01-07 00:16:23Z

0

Option 1

Cast to any
Cast to keyof typeof

Example:

const options = { '-a': 'Alpha', '-o': 'Omega' }
let strOptions = 'Options are:'

for (const k in options) {
  const kAny: any = k
  const key: (keyof typeof options) = kAny

  strOptions += `\n${ key } => ${ options[ key ] }`
}

Option 2:

Use a map

const options = new Map([
  ['-a', 'Alpha'],
  ['-o', 'Omega'],
])

let strOptions = 'Options are:'

options.forEach((v, k) => {
  strOptions += `\n${ k } => ${ v }`
})

edited Jan 7, 2024 at 0:16

answered Jan 6, 2024 at 23:26

gmustudent

2,2296 gold badges33 silver badges45 bronze badges

Collectives™ on Stack Overflow

No index signature with a parameter of type 'string' was found on type '

2 Answers 2

1 Comment

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related