What steps can be taken to dismiss a "TS2531: Object is possibly 'null'" error as a false positive if the object is always guaranteed to not be null?

Here is the code snippet:

const infinoteUrl =
  $q.localStorage.getItem("infinote-dev-api") === null
    ? `${window.location.protocol}//${window.location.host}`
    : $q.localStorage.getItem("infinote-dev-api")
console.log(`infinote URL: ${infinoteUrl}`)

let infinoteToken = $q.localStorage.getItem("infinote-token")
if (infinoteToken === null && !infinoteUrl.toString().includes("localhost")) {
   ...
}

This triggers a 

TS2531: Object is possibly 'null'
error:

TS2531: Object is possibly 'null'.
    106 |
    107 |     let infinoteToken = $q.localStorage.getItem("infinote-token")
  > 108 |     if (infinoteToken === null && !infinoteUrl.toString().includes("localhost")) {
        |                                    ^^^^^^^^^^^
    109 |       infinoteToken = "empty"
    110 |       $q.notify({
    111 |         message: 'no infinote-token in local storage',

I am confident that infinoteUrl cannot be null, and I want to inform the compiler about this specific case. Is there a method to do so?

To address the issue, I utilized Optional Chaining (

if (infinoteToken === null && !infinoteUrl?.toString().includes("localhost"))
). However, I am curious about how to instruct the TS compiler that an identified case is a false positive.

typescriptcompiler-errors

Answer №1

You have the option to utilize the non-null assertion operator, denoted by !. For more information on this operator, you can visit the following link: non-null assertion operator.

If the variable infinoteToken is equal to null and the condition !infinoteUrl!.toString().includes("localhost") is met:

Answer №2

It seems you are assuming that infinoteUrl cannot be null, based on the assumption that 

$q.localStorage.getItem("infinote-dev-api")
will always return the same value twice. However, this is not guaranteed by syntax. That's why TypeScript is issuing a warning. While using !. as suggested may solve the issue, it might go against the purpose of having a strict type system in the first place. It's worth exploring the features provided by TypeScript. You could rewrite it like this:

const maybeInfinoteUrl = $q.localStorage.getItem("infinote-dev-api");
const infinoteUrl =
   maybeInfinoteUrl === null
    ? `${window.location.protocol}//${window.location.host}`
    : maybeInfinoteUrl
console.log(`infinote URL: ${infinoteUrl}`)

Alternatively, a simpler form (which essentially compiles to something similar) would be:

const infinoteUrl =
  $q.localStorage.getItem("infinote-dev-api")
    ?? `${window.location.protocol}//${window.location.host}`

console.log(`infinote URL: ${infinoteUrl}`)

You can try out a TypeScript Playground example here: here.

Answer №3

Check out the @ts-ignore feature for handling errors in TypeScript files.

// @ts-ignore TS2531: Object is possibly 'null'
if (infinoteToken === null && !infinoteUrl.toString().includes("localhost"))

Using this will suppress all errors on the line below the comment, providing a safer way to implement optional chaining even though the value is never null.

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