fetch-api

JavaScript fetch – Failed to execute ‘json’ on ‘Response’: body stream is locked

I met this error too but found out it is not related to the state of Response, the real problem is that you only can consume Response.json() once, if you are consuming it more than once, the error will happen. like below: fetch(‘http://localhost:3000/movies’).then(response =>{ console.log(response); if(response.ok){ console.log(response.json()); //first consume it in console.log return response.json(); //then … Read more

React cannot read property map of undefined

Cannot read property ‘map’ of undefined, Why? Because this.state is initially {}, and contacts of {} will be undefined. Important point is, componentDidMount will get called after initial rendering and it is throwing that error during first rendering. Possible Solutions: 1- Either define the initial value of contacts as [] in state: constructor(props) { super(props) … Read more

fetch retry request (on failure)

From the fetch docs : fetch(“https://stackoverflow.com/users”) .then(checkStatus) .then(parseJSON) .then(function(data) { console.log(‘succeeded’, data) }).catch(function(error) { console.log(‘request failed’, error) }) See that catch? Will trigger when fetch fails, you can fetch again there. Have a look at the Promise API. Implementation example: function wait(delay){ return new Promise((resolve) => setTimeout(resolve, delay)); } function fetchRetry(url, delay, tries, fetchOptions = … Read more

how to process fetch response from an ‘opaque’ type?

Essentially, you cannot access response body from an opaque request. Adding mode: ‘no-cors’ won’t magically make things work. Browsers by default block frontend code from accessing resources cross-origin. If a site sends Access-Control-Allow-Origin in its responses, then browsers will relax that blocking and allow your code to access the response. But if a site doesn’t … Read more

Javascript: Fetch DELETE and PUT requests

Here is a fetch POST example. You can do the same for DELETE. function createNewProfile(profile) { const formData = new FormData(); formData.append(‘first_name’, profile.firstName); formData.append(‘last_name’, profile.lastName); formData.append(’email’, profile.email); return fetch(‘http://example.com/api/v1/registration’, { method: ‘POST’, body: formData }).then(response => response.json()) } createNewProfile(profile) .then((json) => { // handle success }) .catch(error => error);

How do I download a file from FastAPI backend using Fetch API in the frontend?

First, you need to adjust your endpoint on server side to accept path parameters, as in the way it is currently defined, lat and long are expected to be query parameters; however, in your javascript code you are trying to send those coordinates as path parameters. Thus, your endpoint should look like this: @app.get(“/{lat}/{long}/”) async … Read more

Empty body in fetch POST request

The issue is mode: ‘no-cors’ From the documentation… Prevents the method from being anything other than HEAD, GET or POST, and the headers from being anything other than simple headers The simple content-type header restriction allows text/plain, application/x-www-form-urlencoded, and multipart/form-data This causes your nicely crafted Content-Type: application/json header to become content-type: text/plain (at least when … Read more