Using a Type Guard in Typescript to check if an environment variable matches a key in a JSON object

Question

Using a Type Guard in Typescript to check if an environment variable matches a key in a JSON object

I am currently working on creating a Type Guard to prevent TypeScript from throwing an error on the final line, where I attempt to retrieve data based on a specific key. TypeScript is still identifying the environment variable as a string rather than a recognized key of the object. As a result, it is throwing the following error:

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

.

Is there a possibility that I am overlooking a scenario where the environment variable may still be undefined as a key?

import JsonData from '../data/data.json'

const doesKeyExist: (
  input: string | undefined
) => boolean = (input) =>
  input && JsonData.hasOwnProperty(input)

if (!doesKeyExist(process.env.SOME_VARIABLE))
  throw Error('Environment Variable not declared!')

const data = JsonData[process.env.NEXT_PUBLIC_TENANT_ID]

json typescript typeguards

Answer 1

Answer №1

Here is a solution that seems to work:

import jsonData from '../data/data.json'

function checkKeyExistence(
  input: string | undefined
): input is keyof typeof categoriesData {
  return !!(input && categoriesData.hasOwnProperty(input))
}

if (!checkKeyExistence(process.env.SOME_VARIABLE))
  throw Error('Environment Variable not found or the key does not exist in the configuration file!')

const data = jsonData[process.env.NEXT_PUBLIC_TENANT_ID]

Answer 2

Here is a solution that seems to work:

import jsonData from '../data/data.json'

function checkKeyExistence(
  input: string | undefined
): input is keyof typeof categoriesData {
  return !!(input && categoriesData.hasOwnProperty(input))
}

if (!checkKeyExistence(process.env.SOME_VARIABLE))
  throw Error('Environment Variable not found or the key does not exist in the configuration file!')

const data = jsonData[process.env.NEXT_PUBLIC_TENANT_ID]

Using a Type Guard in Typescript to check if an environment variable matches a key in a JSON object

Answer №1

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