Using React Native, it is not possible to include headers in a fetch API request

Question

Using React Native, it is not possible to include headers in a fetch API request

Currently, I am utilizing the Fetch API in react-native along with typescript. The code snippet I am working with looks like this:

let responseLogin = await fetch('http://url_example', {
        method: 'POST',
        headers: {'Content-Type':'application/json'},
        body: requestBody
    });

However, upon running the code, I encounter an error related to the header section:

 Argument of type '{ method: string; headers: { 'Content-Type': string; }; body: string; }' is not assignable to parameter of type 'RequestInit'.
  Types of property 'headers' are incompatible.
    Type '{ 'Content-Type': string; }' is not assignable to type 'Headers | string[][]'.
      Object literal may only specify known properties, and ''Content-Type'' does not exist in type 'Headers | string[][]'.

I have attempted creating a custom header as well but unfortunately, it did not yield any positive results:

    let requestHeaders = new Headers();
        requestHeaders.set('Content-Type', 'application/json');
        // Additional attempt that was made but didn't resolve the issue 
        // requestHeaders.get('Content-Type');

Is there a way to successfully add a header in this scenario? I've tried various methods without success and cannot pinpoint the exact cause of the problem. While testing in postman yields a 200 response, executing the code produces a 401 response. I also experimented by using the library 'fetch-headers' to include custom headers: https://www.npmjs.com/package/fetch-headers

Tools being used: Visual studio code version 1.81.1 "react-native": "0.50.0", "typescript": "2.6.1"

json typescript react-native fetch-api

Answer 1

Answer №1

Could you attempt entering it as HeadersInit?

const requestHeaders: HeadersInit = new Headers();
requestHeaders.set('Content-Type', 'application/json');

const responseLogin = await fetch('URL', {
  method: 'POST',
  headers: requestHeaders,
  body: requestBody
});

If that doesn't work, can you please share the error message you receive when trying to initialize it with the Headers() constructor mentioned in your original question?

Answer 2

Could you attempt entering it as HeadersInit?

const requestHeaders: HeadersInit = new Headers();
requestHeaders.set('Content-Type', 'application/json');

const responseLogin = await fetch('URL', {
  method: 'POST',
  headers: requestHeaders,
  body: requestBody
});

If that doesn't work, can you please share the error message you receive when trying to initialize it with the Headers() constructor mentioned in your original question?

Answer 3

Answer №2

Which TypeScript libraries have been integrated into your project's build process? It seems like there may be an issue with how you've defined the headers property. According to TypeScript 2.6.2 specifications, the correct type for the headers property should be HeadersInit, as outlined below:

type HeadersInit = Headers | string[][] | { [key: string]: string };

Answer 4

Which TypeScript libraries have been integrated into your project's build process? It seems like there may be an issue with how you've defined the headers property. According to TypeScript 2.6.2 specifications, the correct type for the headers property should be HeadersInit, as outlined below:

type HeadersInit = Headers | string[][] | { [key: string]: string };

Answer 5

Answer №3

To resolve the issue, I successfully tackled it by bringing in the Headers module through this method:

import fetch, { Headers } from 'node-fetch';

Answer 6

To resolve the issue, I successfully tackled it by bringing in the Headers module through this method:

import fetch, { Headers } from 'node-fetch';

Answer 7

Answer №4

The solution provided in the accepted answer lacks handling for a specific scenario where the fetch function is encapsulated within a custom function that takes the same arguments as fetch and sets defaults for the headers property. Here's an example:

async function myFetch(input: RequestInfo, init: RequestInit) {
  // set default headers
  const res = await fetch(input, init)
  // handle response and errors here
}

The issue with this approach is that the type of RequestInit.headers is defined as HeadersInit, which can be of various types such as string arrays, key-value pairs, or Headers objects.

To address this, I created a custom MyRequestInit type where the headers property is strictly defined as Record<string, string>. This simplifies the handling of headers to just an object with string key-value pairs.



export interface MyRequestInit extends Omit<RequestInit, 'headers'> {
  headers?: Record<string, string>;
}

export async function fetchJson<JSON = unknown>(
  input: RequestInfo,
  init: MyRequestInit = {},
) {
  // set default headers
  const res = await fetch(input, init)
  // process response
}

Answer 8

The solution provided in the accepted answer lacks handling for a specific scenario where the fetch function is encapsulated within a custom function that takes the same arguments as fetch and sets defaults for the headers property. Here's an example:

async function myFetch(input: RequestInfo, init: RequestInit) {
  // set default headers
  const res = await fetch(input, init)
  // handle response and errors here
}

The issue with this approach is that the type of RequestInit.headers is defined as HeadersInit, which can be of various types such as string arrays, key-value pairs, or Headers objects.

To address this, I created a custom MyRequestInit type where the headers property is strictly defined as Record<string, string>. This simplifies the handling of headers to just an object with string key-value pairs.



export interface MyRequestInit extends Omit<RequestInit, 'headers'> {
  headers?: Record<string, string>;
}

export async function fetchJson<JSON = unknown>(
  input: RequestInfo,
  init: MyRequestInit = {},
) {
  // set default headers
  const res = await fetch(input, init)
  // process response
}

Answer 9

Answer №5

I encountered a similar issue, but the solution provided did not work for me because headers may have already been initialized. Therefore,

    if (!requestInit.headers) {
      requestInit.headers = new Headers()
    }

    requestInit.headers.set('Content-Type', 'application/json')
    // *TS2339: Property 'set' does not exist on type 'HeadersInit'. Property 'set' does not exist on type 'string[][]'*

This results in a compilation error, as mentioned by others, because HeadersInit is defined as

type HeadersInit = string[][] | Record<string, string> | Headers;

SOLUTION: use constructor with parameter

requestInit.headers = new Headers(requestInit.headers)
requestInit.headers.set('Content-Type', 'application/json')

Answer 10

I encountered a similar issue, but the solution provided did not work for me because headers may have already been initialized. Therefore,

    if (!requestInit.headers) {
      requestInit.headers = new Headers()
    }

    requestInit.headers.set('Content-Type', 'application/json')
    // *TS2339: Property 'set' does not exist on type 'HeadersInit'. Property 'set' does not exist on type 'string[][]'*

This results in a compilation error, as mentioned by others, because HeadersInit is defined as

type HeadersInit = string[][] | Record<string, string> | Headers;

SOLUTION: use constructor with parameter

requestInit.headers = new Headers(requestInit.headers)
requestInit.headers.set('Content-Type', 'application/json')

Answer 11

Answer №6

In the year 2024, your inquiry remains relevant and now there is an option to convert the item you provide as a HeadersInit:

let responseLogin = await fetch('http://url_example', {
        method: 'POST',
        headers: {'Content-Type':'application/json'} as HeadersInit,
        body: requestBody
    });

Personally, I have found that by using this cast, the error messages from tsc no longer persist. Although, it should be noted that my analysis was conducted with tsc version 5.6.3 rather than 2.6.

Answer 12

In the year 2024, your inquiry remains relevant and now there is an option to convert the item you provide as a HeadersInit:

let responseLogin = await fetch('http://url_example', {
        method: 'POST',
        headers: {'Content-Type':'application/json'} as HeadersInit,
        body: requestBody
    });

Personally, I have found that by using this cast, the error messages from tsc no longer persist. Although, it should be noted that my analysis was conducted with tsc version 5.6.3 rather than 2.6.

Using React Native, it is not possible to include headers in a fetch API request

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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