What is the best approach to managing a 204 status in Typescript in conjunction with the Fetch API

Struggling to handle a 204 status response in my post request using fetch and typescript.

I've attempted to return a promise with a null value, but it's not working as expected.

    postRequest = async <T>(url: string, body: any): Promise<T> => {
        const response = await fetch(url, {
            method: 'POST',
            headers: {
                'Content-Type': 'application/json;charset=utf-8'
            },
            body: JSON.stringify(body)
        });

        // I'm facing an issue here
        if (response.status === 204) {
            // error is: "Type 'null' is not assignable to type 'T'."
            return null;
            // I have tried returning a promise, but it doesn't work.
            // error is: "Argument of type 'null' is not assignable to 
            // parameter of type 'T | PromiseLike<T> | undefined'."
            return new Promise(resolve => resolve(null));
        }

        if (!response.ok) {
            throw new Error(response.statusText);
        }

        return await response.json() as Promise<T>;
    };


    postRequest<{data: boolean}>('request', { someValue: 1234 });

Answer №1

To show that a Union Type is used to define that either a Promise<T> or a Promise<null> is returned:

postRequest = async <T>(url: string, body: any): Promise<T | null> => {

In this instance, the return type specified is Promise<T | null>, indicating that either T or null will be employed for a fulfilled promise.

Answer №2

To make your function able to return null values, simply include it in the return type.

postRequest = async <T>(url: string, body: any): Promise<T|null> => {
...
}

Furthermore, there's no need to await the return value within an async function since the promise takes care of that automatically:

return response.json() as T;

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