I have a function called create(conn, params) in my controller that gets called when some data is posted to my server from a form on the client – the form was built using Phoenix templates.

All I do is extract some data from the params, do something with it, and then render another template in response.

Now I would like to write myself a little javascript helper function so that I can click something in my browser and have this data posted from JS – i.e., I just want to post the same data I would otherwise post, except without going through the form.

Everything seems to work, I can see the data arriving at my server, and the params are what I expect. But no response is ever rendered.

code inside my create(conn, params) function looks like this:

    IO.inspect("I get this far okay")
    conn
    |> put_flash(:info, "Found ID: #{the_id}")
    |> render("confirm_sheet.html", title: title, some_data: some_data)

I don’t see any error message on the server or client – it’s like my code just prints out “I get this far okay” and then vanishes into thin air.

But then if I go post the data from my form, I see the response in the confirm_sheet.html template as expected.

The only difference I can think of is that I am posting JSON instead of some other format. Here is the JS function that I am using to try to call my route:

<script>
    window.quick_post = function(gsheet_id) {
        var xhr = new XMLHttpRequest();
        xhr.open("POST", "http://localhost:4000/sheets", true);
        xhr.setRequestHeader('Content-Type', 'application/json');
        xhr.setRequestHeader('Accept', 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8');
        var to_send = JSON.stringify({
            "_csrf_token": "<%= Phoenix.Controller.get_csrf_token() %>",
            "sheet": {"the_id": the_id}
        });
        xhr.send(to_send);
    }
</script>

So what is happening here? How can a route give no error / warning and also no response?