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Check if POST was successful and then run JavaScript

How do I check, if a POST XHR request was successful, on a website, for a particular URL?
If the POST was successful, I then want to run some JavaScript.
I've seen ways to do this in jQuery, but I want to do this via vanilla JavaScript.

You can use the status code to check if the request was successful:
var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
if (xhr.readyState == XMLHttpRequest.DONE && xhr.status == 200) {
// successful
}
}
xhr.open('GET', 'http://example.com', true);
xhr.send();
https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/status
https://stackoverflow.com/a/3038972/10551293

Writing Request Payload property on httprequest

I am trying to develop a browser extension that will help people to some stuff way easier.
One of the things that I need to do is sending couple of http requests.
I need to recreate requests that site makes when doing certain things.
Now site uses Request Payload which is my first time using(used form data),therefore I don't know how to make Request Payload same as when site sends request.
var request = new XMLHttpRequest(),
url = 'https://www.hidden.com/api/v1/tipuser/',
data = 'steam_64=76561198364912967&tip_asset_ids=[]&tip_balance=0',
token ='...';
request.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
console.log("The request and response was successful!");
}
};
request.open('POST', url, true);
request.setRequestHeader('Content-type', 'text/plain');
request.setRequestHeader('authorization', token);
request.send(data);
This is my code and after sending it you can see how my Request Payload looks.
I have been having difficulties for days now and I searched online but couldn't find solution to this.I know that I just have to write it differently .
This is site's request
This is my request
Cheers!

Could you try sending your request as application/json and build your data object like in the example below?
Your Content-type request header should be application/json
var request = new XMLHttpRequest(),
url = 'https://jsonplaceholder.typicode.com/posts/',
data = {
steam_64: '76561198364912967',
tip_asset_ids: [],
tip_balance: 0,
token: '',
};
request.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
console.log("The request and response was successful!");
}
};
request.open('POST', url, true);
request.setRequestHeader('Content-type', 'application/json');
request.setRequestHeader('authorization', data.token);
request.send(JSON.stringify(data));

Ajax response not coming through from node.js

My Ajax request is not receiving proper response! It always enters readyState '4' with response status '0' ??
Client Code:
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function(){
if(xhttp.readyState == 4 && xhttp.status == 200){
document.getElementById("lastNameLabel").innerHTML = "response recieved!";
const responseJSON = JSON.parse(xhttp.responseText);
if(responseJSON.emailTaken == "false"){
window.location = server+"/client/home.html";
}
}
};
xhttp.open("POST", server+"/signUp", true);
xhttp.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhttp.send("email="+email);
server Code (Node.js + Express):
app.post('/signUp', (req, res) => {
res.end("it worked!!");
});
I Know my Server is processing the request since I see the url call, but the response never reaches the html client!!. I'm Super Stuck!

Putting #jaromanda-x's suggestion as an answer, you need to enable CORS in your server.
This is how it's done:
var cors = require('cors');
app.use(cors());
For more info, refer this express doc about it.

You have to have your NodeJS server reply with an HTTP response message that includes a status code and reason phrase such as
res.status(200).send({ status: 'ok' });

Setting up CORS not working

I have the following headers set on the server
response.addHeader("Access-Control-Allow-Origin", "*");
response.addHeader("Access-Control-Allow-Methods", "GET, POST, PUT");
response.addHeader("Access-Control-Allow-Headers","X-Custom-Header");
And i want to use the POST method to access a web service and send data to it but the problem is my setting up with the server is causing problems
I used the following method
function createCORSRequest(method, url) {
var xhr = new XMLHttpRequest();
if ("withCredentials" in xhr) {
// XHR for Chrome/Safari/Firefox.
xhr.open(method, url, true);
}
else if (typeof XDomainRequest != "undefined") {
// XDomainRequest for IE.
xhr = new XDomainRequest();
xhr.open(method, url);
} else {
// CORS not supported.
xhr = null;
}
return xhr;
}
and based on this object
url = "http://myurl.do";
var xhr = createCORSRequest('POST', url);
if (!xhr) {
alert('CORS not supported');
return;
}
var params = "name=pari123&action=initaction&gameId=slotreel3";
xhr.setRequestHeader('Content-Type', 'application/text/plain');
if(xhr.readyState == 4 && xhr.status == 200)
{
alert('Tested OK')
xhr.send(params);
}
else
{
alert('status not 200 or xhr is not ready');
}
// Response handlers.
xhr.onload = function() {
var text = xhr.responseText;
alert('Response from CORS request to ' + url + ': ' + text);
};
xhr.onerror = function() {
alert('Woops, there was an error making the request.');
};
But always it alerts a message saying 'status not 200 or xhr is not ready' i am not able to proceed any one if you know please kindly help!
when i print the xhr.readyState its printing a value of 1

if(xhr.readyState == 4 && xhr.status == 200)
This check must be placed in the onreadystatechange event handler. You obviously cannot have a 200 status code or a "finished" request before actually sending it.
What you wanted is probably this:
xhr.onreadystatechange = function() {
if(xhr.readyState == 4 && xhr.status == 200) {
alert('Tested OK');
var text = xhr.responseText;
alert('Response from CORS request to ' + url + ': ' + text);
}
};
xhr.send(params);
If you want an else case to check for errors remember that you still need to check for xhr.readyState == 4. You don't want your error-handling code to run for other readyStates.
There is no need for the onload event - when you get readyState == 4 you know the request has finished.

There can be several issues here.
I observed that different browsers implement CORS differently. My experience is based on Firefox and Google Chrome. For example, I had to add a special header on server side, so that Firefox would make the preflight (OPTIONS) request and the actual request (GET,PUT etc.) using one connection as Google Chrome does it. You would have to add on the server side:
response.addHeader("Keep-Alive", "timeout=2, max=100");
response.addHeader("Connection", "Keep-Alive");
I also noticed that some browsers do not like the wildcard ("*") in the CORS headers. A workaround for the line
response.addHeader("Access-Control-Allow-Origin", "*");
would be to return the origin of the request and not a wildcard.
However, there could be also other problems and we would need more details. For example, does the request work when the server is hosted on the same domain (i.e. the problem might not be related to CORS). What server are you using?

xhr.send(); needs to be just after the call to xhr.open(); does it not? Status 1 means the request has not been sent yet, it'll never get to status 4 unless you actually send the request..

How to respond to an XMLHttpRequest

I'm using a Javascript to ask our app (which is in Google App Engine) if the file a user wants to upload is already in his list of files (he will overwrite).
I know how to send the request, but how can I create a response from the server, using Python?
This is the request:
var req = new XMLHttpRequest();
req.open('POST', 'https://safeshareapp.appspot.com/upload', async);
req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
req.setRequestHeader("Content-length", body.length);
req.setRequestHeader("Connection", "close");
if (async) {
req.onreadystatechange = function() {
if(req.readyState == 4 && req.status == 200) {
var response = null;
try {
response = JSON.parse(req.responseText);
} catch (e) {
response = req.responseText;
}
callback(response);
}
}
}
// Make the actual request
req.send(body);
As you see, we are getting the responseText from the request after everything has gone OK, but my question is how do we fill that responseText field on the server side??

class MyRequestHandler(webapp.RequestHandler):
def get(self):
import json
result = {"filename": xxx} // just an example, result can be any Python object
json_obj = json.dumps(result)
self.response.out.write(str(json_obj))