Apply same function to different objects in typescript

Issue

Let's say I have a couple of functions (they're GraphQL resolvers but I don't think it's that relevant):

function doSomething: (args: doSomethingInput) => {
  const { id, accessToken, type } = args.input
  // more code here that uses those variables...
}

function doSomethingElse: (args: doSomethingElseInput) => {
  const { id, accessToken, points } = args.input
  // more code here that uses those variables...
}

type doSomethingInput = {
  input: { id: string, accessToken: string, type: string }
}

type doSomethingElseInput = {
  input: { id: string, accessToken: string, points: string }
}

I would like to sanitize the input that's passed to those function, so my idea is to do something like this using the validator library:

import validator from 'validator'

function doSomething: (args: doSomethingInput) => {
  for (const [key, value] of Object.entries(args.input)) {
    const keyTyped = key as keyof typeof args.input
    args.input[keyTyped] = validator.escape(value)
  }

  const { id, accessToken, type } = args.input
  // more code here that uses those variables...
}

This would allow, for example, that an accessToken that was passed as such 28502307<script>alert('HELLO')</script> to my function will then look like this 28502307<script>alert('HELLO')</script> which I prefer.

However, I would like to apply this to the input of all my resolvers. That's why I would like to write a function to externalize that behavior:

import validator from 'validator'

function sanitize(inputParameters: object): object {
  for (const [key, value] of Object.entries(inputParameters)) {
    inputParameters[key] = validator.escape(value as string)
  }

  return inputParameters
}

However it gives me this error:

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

And this doesn't work either:

import validator from 'validator'

function sanitize(inputParameters: object): object {
  for (const [key, value] of Object.entries(inputParameters)) {
    const keyTyped = key as keyof typeof inputParameters
    inputParameters[keyTyped] = validator.escape(value as string)
  }

  return inputParameters
}

this time with this error:

Type 'string' is not assignable to type 'never'.

(I found that typecast line somewhere else in here in stackoverflow)

So, how can apply a generic function to objects with different types?

Solution

I don't know what your inputParameters will contain, but you cannot access arbitrary keys of object type (see this answer). So instead I recommend you use the Record type with any as key (allowing any string or number key) and unknown value type (allows for any value, but continues to check the type).

If you don't know inputParameters value types ahead of time, you might want to check them first, since using as assertion (value as string) just disabled most of typescript checks and can lead to undesired consequences. Instead you can check if value is a string with typeof value === 'string' and if it's not, ignore the value (or go deeper if the value itself is a Record).

---

Here's the sanitize function with Record type:

function sanitize(inputParameters: Record<any, unknown>): Record<any, unknown> {
  for (const [key, value] of Object.entries(inputParameters)) {
    inputParameters[key] = validator.escape(value as string)
  }

  return inputParameters
}

More on Record in the typescript docs,

Answered By - Murolem