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Submit POST Form Data With JavaScript

April 2025

Introduction

I'm working on a personal browser extension1 for my Grimoire2. I need it to send data to the local server that provides the backend3. This is how I'm doing that:

HTML

<button id="submit-button">Submit</button>
<pre id="output">waiting...</pre>

Output

waiting...
JavaScript
async function sendData(data) {
  const postUrl = "https://echo.hoppscotch.io/";
  const bodyData = JSON.stringify({ 
    "key1": "alfa",
    "key2": "bravo",
  });
  try {
    const response = await fetch(
      postUrl, {
      method: "POST",
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json'
      },
      body: bodyData,
    });
    const result = await response.json();
    showOutput(result);
  } catch (e) {
    console.error(e);
  }
}

function showOutput(data) {
  const outputEl = document.querySelector(
    "#output"
  );
  outputEl.innerHTML = JSON.stringify(
    data, null, 2
  );
}

const sender = document.querySelector(
  "#submit-button"
);

sender.addEventListener(
  "click", sendData
);

Notes

  • The code on this page is live. If you click the Submit button, it'll run. Assuming the service it's connected to is running, you'll see a response update the <pre id="output"> element.
  • The sendData function is attached to the click handler of the #submit-button.
  • When sendData is triggered it sends a POST request to https://echo.hoppscotch.io with the parameters defined in bodyData
  • The JSON response is stringified and output in <pre id="output"> when it's returned. The payload is an echo which shows the original parameters along with some metadata.
end of line

Footnotes

1 ⤴

The idea is to add functionality to the browser so I can open a little window on any page and use it to make a bookmark, grab a quote, or collect videos directly into my Grimoire.

2 ⤴

Some call it a notes app. I call it a book of magic.

3 ⤴

The backend I'm building that will let me add a bunch of automation to my Grimoire.