What methods can be used to determine the specific object returned by an API when working with typescript?

Question

What methods can be used to determine the specific object returned by an API when working with typescript?

When retrieving customer information from Stripe, there are three possible object types that can be returned. Typically, I am interested in obtaining the customer ID.

The code snippet below might not be the most elegant solution to handle this scenario.

Is there a more efficient and cleaner way to achieve this?

  const stripeCustomer: string | Stripe.Customer | Stripe.DeletedCustomer = checkoutSession.customer;
  let stripeCustomerId: string;

  if (stripeCustomer instanceof Object && "email" in stripeCustomer) {
    // The customer is of type 'Stripe.Customer'
      stripeCustomerId = stripeCustomer.id;
  } else if (typeof stripeCustomer === 'string') { 
    // The customer is an ID
    stripeCustomerId = stripeCustomer;
  } else {
    // The customer is of type 'Stripe.DeletedCustomer'
    stripeCustomerId = null;
  }

typescript stripe-payments

Answer 1

Answer №1

If you want to implement custom type-checking logic into the type system, you can utilize user-defined type guards. These guards help in identifying the specified type for an object when certain conditions are met:

function isStripeCustomer(object: any): object is Stripe.Customer {
    return object instanceof Object 
       && "object" in object 
       && object.object === 'customer' 
       && !object.deleted
}

function isStripCustomerID(object: any): object is string {
    return typeof object === "string";
}

function isStripeDeletedCustomer(object: any): object is Stripe.DeletedCustomer {
    return object instanceof Object
       && "object" in object 
       && object.object === 'customer' 
       && object.deleted
}

const customer: string | Stripe.Customer | Stripe.DeletedCustomer = checkoutSession.customer;

let stripeCustomerId: string | null

if (isStripeCustomer(customer)) {
    stripeCustomerId = customer.id
} else if (isStripCustomerID(customer)) { 
    stripeCustomerId = customer;
} else if (isStripeDeletedCustomer(customer) {
    stripeCustomerId = null;
} else {
    // It was none of the known types. Perhaps a new type of result was
    // add in a future version of their API?

}

Answer 2

If you want to implement custom type-checking logic into the type system, you can utilize user-defined type guards. These guards help in identifying the specified type for an object when certain conditions are met:

function isStripeCustomer(object: any): object is Stripe.Customer {
    return object instanceof Object 
       && "object" in object 
       && object.object === 'customer' 
       && !object.deleted
}

function isStripCustomerID(object: any): object is string {
    return typeof object === "string";
}

function isStripeDeletedCustomer(object: any): object is Stripe.DeletedCustomer {
    return object instanceof Object
       && "object" in object 
       && object.object === 'customer' 
       && object.deleted
}

const customer: string | Stripe.Customer | Stripe.DeletedCustomer = checkoutSession.customer;

let stripeCustomerId: string | null

if (isStripeCustomer(customer)) {
    stripeCustomerId = customer.id
} else if (isStripCustomerID(customer)) { 
    stripeCustomerId = customer;
} else if (isStripeDeletedCustomer(customer) {
    stripeCustomerId = null;
} else {
    // It was none of the known types. Perhaps a new type of result was
    // add in a future version of their API?

}

Answer 3

Answer №2

Your approach is on the right track. By implementing typeguards, you can ensure type-safety and catch potential issues during compile-time:

interface Customer {
    id: string;
}

type CustomerResponse = Customer | string | null;

function isCustomerObject(customer: CustomerResponse): customer is Customer {
    return customer != null && typeof customer === "object" && customer.id != null;
}

function isString(str: CustomerResponse): str is string {
    return typeof str === "string";
}

function identify(obj: Customer | string | null) {
    if (isCustomerObject(obj)) {
        console.log(obj, "is a customer with ID", obj.id);
    } else if (isString(obj)) {
        console.log(obj, "is a string with value", obj);
    } else {
        console.log(obj, "is null");
    }
}

const customerObject: Customer = {
    id: "123"
};


identify(customerObject);
identify("123");
identify(null);

To experiment with this code further, check out the TypeScript Playground version of the code.

Answer 4

Your approach is on the right track. By implementing typeguards, you can ensure type-safety and catch potential issues during compile-time:

interface Customer {
    id: string;
}

type CustomerResponse = Customer | string | null;

function isCustomerObject(customer: CustomerResponse): customer is Customer {
    return customer != null && typeof customer === "object" && customer.id != null;
}

function isString(str: CustomerResponse): str is string {
    return typeof str === "string";
}

function identify(obj: Customer | string | null) {
    if (isCustomerObject(obj)) {
        console.log(obj, "is a customer with ID", obj.id);
    } else if (isString(obj)) {
        console.log(obj, "is a string with value", obj);
    } else {
        console.log(obj, "is null");
    }
}

const customerObject: Customer = {
    id: "123"
};


identify(customerObject);
identify("123");
identify(null);

To experiment with this code further, check out the TypeScript Playground version of the code.

What methods can be used to determine the specific object returned by an API when working with typescript?

Answer №1

Answer №2

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