Is your Typescript compilation running into a problem with jwt tokens?

Question

Is your Typescript compilation running into a problem with jwt tokens?

Having issues while trying to compile a typescript file as the compiler is throwing an error message:

Error: TS2339 - The property 'payload' does not exist on type 'string | object'.
  Property 'payload' does not exist on type 'string'.

Here is the problematic code:

decode(token: string): any {
  const decodedJWT = jwt.decode(token, { complete: true });

  const issuer = decodedJWT.payload.iss;
                           ^^^^^^^^^
  return {};
}

I have utilized the @types/jsonwebtoken library for defining the types. Any assistance in resolving this issue would be highly appreciated.

typescript json-web-token

Answer 1

Answer №1

The error you're encountering stems from TypeScript's type checking. The return type of jwt.decode() can be either null, object, or string. If you are confident that jwt.decode() will always return an object, you can use a type cast to any on decodedJWT to prevent this error:

decode(token: string): any {
  const decodedJWT = jwt.decode(token, { complete: true });

  const issuer = (decodedJWT as any).payload.iss;
  return {};
}

In the code snippet above, there is a potential for exceptions at runtime because jwt.decode() could potentially return null or a string. Only an object will have the payload property. It is advisable to handle the return value in a more cautious manner:

decode(token: string): any {
  const decodedJWT = jwt.decode(token, { complete: true });

  if (decodedJWT === null) {
       // handle null case
  } else if (typeof decodedJWT === 'string') {
       // handle string case
  } else {
       const issuer = (decodedJWT as any).payload.iss; // type cast to `any`
  }

  return {};
}

Answer 2

The error you're encountering stems from TypeScript's type checking. The return type of jwt.decode() can be either null, object, or string. If you are confident that jwt.decode() will always return an object, you can use a type cast to any on decodedJWT to prevent this error:

decode(token: string): any {
  const decodedJWT = jwt.decode(token, { complete: true });

  const issuer = (decodedJWT as any).payload.iss;
  return {};
}

In the code snippet above, there is a potential for exceptions at runtime because jwt.decode() could potentially return null or a string. Only an object will have the payload property. It is advisable to handle the return value in a more cautious manner:

decode(token: string): any {
  const decodedJWT = jwt.decode(token, { complete: true });

  if (decodedJWT === null) {
       // handle null case
  } else if (typeof decodedJWT === 'string') {
       // handle string case
  } else {
       const issuer = (decodedJWT as any).payload.iss; // type cast to `any`
  }

  return {};
}

Is your Typescript compilation running into a problem with jwt tokens?

Answer №1

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