Adding custom headers in Javascript for all http requests

Question

I want to add custom headers (Bearer token) to each http call in a ASP.Net Web Form application.

Using the recommendations in the following links, I added the code to send added headers to the server to no avail.

How to intercept all http requests including form submits

and

<script>
    (function() { 
        (function (open) {
            XMLHttpRequest.prototype.open = function (method, url, async, user, password) {
                console.log("Adding header");
                open.call(this, method, url, async, user, password);
                this.setRequestHeader("X-Hello", "There " + new Date());
            };
        })(XMLHttpRequest.prototype.open);
    })();
</script>

And

<script>
    (function() { 
        (function (send) {
            XMLHttpRequest.prototype.send = function (data) {
                console.log("Adding header");
                this.setRequestHeader("X-Hello", "There");
                send.call(this, data);
            };
        })(XMLHttpRequest.prototype.send);
    })();
</script>

I understand that the solution is supposed to work only for the POSTs (but it doesn't.) I do see the console.log for every post, yet the header, "X-Hello" never shows on the server side.

The long solution using the service worker failed on:

return Promise.resolve(new Request(data.url, data));

"Failed to construct 'Request': Cannot construct a Request with a Request whose mode is 'navigate' and a non-empty RequestInit."

score 9 · Answer 1 · answered Feb 22 '21 at 13:00

9

Try this:-

XMLHttpRequest.prototype.open = (function(open) {
  return function(method,url,async) {
    open.apply(this,arguments);
    this.setRequestHeader('customHeader1', 'someValue');
    this.setRequestHeader('customHeader2', 'someOtherValue');
    };
})(XMLHttpRequest.prototype.open);

answered Feb 22 '21 at 13:00

Vivek Prasad

91
1
1

3

While this code may provide a solution to the question, it's better to add context as to why/how it works. This can help future users learn and eventually apply that knowledge to their own code. You are also likely to have positive-feedback/upvotes from users, when the code is explained. – Amit Verma Feb 22 '21 at 13:51

score 6 · Answer 2 · answered Jul 08 '19 at 19:29

One way to do this would be to use a service worker. However this method is not supported by all browsers, so watch your audience. With a service worker, you would intercept all the fetch requests that go through the browser. however browsers will only allow you to send custom headers for urls related to the current origin. With that in mind, here's a code sample.

//This is the fetch event listener
self.addEventListener("fetch", (event) => {
    var currentUrl = new URL(event.request.url);
    if (currentUrl.origin === location.origin){
        var newRequest = new Request(event.request, {
            mode: "cors",
            credentials: "same-origin",
            headers: {
                YOUR_CUSTOM_HEADER_NAME: YOUR_CUSTOM_HEADER_VALUE,
            }
        });
        event.respondWith(fetch(newRequest));
    }
    else {
        event.respondWith(fetch(event.request));
    }
});

Also if you use a constant, variable to store the headers value and name, the browser will take the name of the variable(in lower case) as the header name(not it's value).

you can put the variable name in brackets `{ [foo]: var}` to use the value inside of the variable, instead of foo as the key. — run_the_race, Feb 08 '22 at 08:01
This will work for client running in browser right? But can you share a way to track outgoing http calls similar to in server side? For example from express.js ? — Ayush Tiwari, Mar 11 '23 at 16:22

score 1 · Answer 3 · answered May 08 '19 at 12:04

You need to instantiate XMLHttpRequest to use it.

var x = new XMLHttpRequest();
x.open("GET","http://some.url");
x.setRequestHeader("X-Hello","There");
x.send();

You wouldn't use Request directly... that is created internally by the modern fetch(..) API.

fetch("http://some.url",{ method:"GET", headers: { "X-Hello": "There" }})
.then(function onRes(res){
   if (res && res.ok) {
      // ..
   }
});

Adding custom headers in Javascript for all http requests

3 Answers3

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