Can you clarify the meaning of this error message: Uncaught TypeError - Already read?

Question

Can you clarify the meaning of this error message: Uncaught TypeError - Already read?

When does this error occur in Javascript?

https://i.sstatic.net/7y3GP.png

The Error in index.js

/**
 * Created by tushar.mathur on 24/12/15.
 */
'use strict'

const _ = require('lodash')
const Rx = require('rx')
const createDataStore = require('./src/createDataStore')

const fetch = x => Rx.Observable.fromPromise(window.fetch(x)) 
const parseJSON = x => Rx.Observable.fromPromise(x.json()) // Line: 11 (This is where the exception occurs)
var create = _.partial(createDataStore, fetch, parseJSON)
module.exports = {
  create,
  // Alias for legacy purposes
  createDataStore: create,
  createFetchStore: create
}

Is it related to a native promise error? What are the implications of this error? A search on Google yields no relevant results.

javascript promise typeerror

Answer 1

Answer №1

From my understanding, the error occurs when the body has already been read using methods like .json() or .text(). When you call x.json(), it reads the response's body into JSON format. Trying to call x.json() again will result in an error because each of these methods can only be used once. It seems like somewhere in your code, the body of the same response is being read again using one of the Body methods mentioned here.

I believe this is why they provide the Body.bodyUsed method, so you can check if the body has already been read.

Answer 2

From my understanding, the error occurs when the body has already been read using methods like .json() or .text(). When you call x.json(), it reads the response's body into JSON format. Trying to call x.json() again will result in an error because each of these methods can only be used once. It seems like somewhere in your code, the body of the same response is being read again using one of the Body methods mentioned here.

I believe this is why they provide the Body.bodyUsed method, so you can check if the body has already been read.

Answer 3

Answer №2

If you encounter this error, it indicates that the promise has been resolved multiple times (specifically when using Body.json()).

To address this issue, refer to the response body methods in the link provided below and ensure that you use a flag to verify if the promise has already been resolved, such as utilizing Body.bodyUsed.

For more information, please visit: https://developer.mozilla.org/en-US/docs/Web/API/Response

Hope this helps!

Answer 4

If you encounter this error, it indicates that the promise has been resolved multiple times (specifically when using Body.json()).

To address this issue, refer to the response body methods in the link provided below and ensure that you use a flag to verify if the promise has already been resolved, such as utilizing Body.bodyUsed.

For more information, please visit: https://developer.mozilla.org/en-US/docs/Web/API/Response

Hope this helps!

Answer 5

Answer №3

Encountering a similar issue arises with Next.js when making API calls from the client side to the Next.js server, particularly when dealing with form data. If you're seeking guidance on how to manage form data in Next.js (version >= 13), here's an approach that worked for me:

Client

    let formData = new FormData();
    formData.append("file", file, file.name);
    const response = await fetch(`/api/{nextjs_server}`, {
      method: "POST",
      headers: {
        Authorization: `${token if necessary}`,
      },
      body: formData,
      redirect: 'follow'
    });

Server (Next.js)

export const POST = async (req, res) => {
const formDataFlag = await req.formData() // representing the form data sent from the client
  if (formDataFlag) {
    const file = formDataFlag.get('file');
    
    const formDataToSend = new FormData();
    formDataToSend.append('file', file, file.name);

    const response = await fetch(`${actual api url}`, {
      method: "POST",
      headers: {
        Authorization: `Bearer ${token if necessary}`,
      },
      body: formDataToSend,
      redirect: 'follow'
    })
    const textResponse = await response.text();
    return new Response(textResponse, { status: 200 });
  }
}

The crucial step is to redefine the form data (in my case, I named it formDataToSend). Happy coding!

Answer 6

Encountering a similar issue arises with Next.js when making API calls from the client side to the Next.js server, particularly when dealing with form data. If you're seeking guidance on how to manage form data in Next.js (version >= 13), here's an approach that worked for me:

Client

    let formData = new FormData();
    formData.append("file", file, file.name);
    const response = await fetch(`/api/{nextjs_server}`, {
      method: "POST",
      headers: {
        Authorization: `${token if necessary}`,
      },
      body: formData,
      redirect: 'follow'
    });

Server (Next.js)

export const POST = async (req, res) => {
const formDataFlag = await req.formData() // representing the form data sent from the client
  if (formDataFlag) {
    const file = formDataFlag.get('file');
    
    const formDataToSend = new FormData();
    formDataToSend.append('file', file, file.name);

    const response = await fetch(`${actual api url}`, {
      method: "POST",
      headers: {
        Authorization: `Bearer ${token if necessary}`,
      },
      body: formDataToSend,
      redirect: 'follow'
    })
    const textResponse = await response.text();
    return new Response(textResponse, { status: 200 });
  }
}

The crucial step is to redefine the form data (in my case, I named it formDataToSend). Happy coding!

Can you clarify the meaning of this error message: Uncaught TypeError - Already read?

Answer №1

Answer №2

Answer №3

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