Typescript error: Type 'undefined' cannot be used as an index type.ts(2538)

[deadcoder0904]

I was following along https://spacejelly.dev/posts/how-to-make-twitter-api-requests-with-nextauth-js-session-tokens/#step-1-accessing-twitter-oauth-tokens-in-a-nextauthjs-session & found this chunk of code written in JS:

callbacks: {
    async jwt({ token, user, account = {}, profile, isNewUser }) {
      if (account.provider && !token[account.provider]) {
        token[account.provider] = {}
      }

      if (account.access_token) {
        token[account.provider].accessToken = account.access_token
      }

      if (account.refresh_token) {
        token[account.provider].refreshToken = account.refresh_token
      }

      return token
    },
  },

On the 2nd & 3rd if statements, I get an error on account.provider:

Type 'undefined' cannot be used as an index type.ts(2538)

I've tried all general methods to fix it using TS like as string or ! but I can't manage to find a fix.

What's the solution for this?

[balazsorban44]

just simplify to one if statement with if(account)

This should work:

async jwt({ token, account }) {
  if (account) {
    token[account.provider] = {
      accessToken: account.access_token,
      refreshToken: account.refresh_token,
    }
  }

  return token
}

Furthermore, to make TS happy, check out the docs at: https://next-auth.js.org/getting-started/typescript#submodules

declare module "next-auth/jwt" {
  interface JWT {
    [key: string]: {
      accessToken: string
      refreshToken: string
    }
  }
}

[deadcoder0904]

Thanks @balazsorban44 that worked. I saw the TS docs but didn't knew what to put inside.