Handling POSTed data from Forms

On the Internet page there was a simple example of sending data in the URL from a webpage, but that can be quite unreliable if anywhere between your browser and the Espruino decides to cache the received data.

To work around this, HTTP provides POST requests, that differ from the normal GET requests in that they signal that data needs to always be sent back to the server.

The code below is broken into 4 main parts:

  • onInit - is run at startup and initialises the WiFi
  • onConnected - is called when there is a WiFi connection, it prints the IP address and starts the Web Server.
  • onPageRequest - handles the webpage request, serving up the HTML for the form, or sending a 404 Page Not Found for unknown URLs
  • handlePOST - is called when data is POSTed to Espruino. It receives all the data, splits it up and decodes it, and finally turns on LEDs based on the data that was received.

You'll Need

A device that'll connect to the Internet, like an Espruino WiFi or a Pico with an ESP8266 attached.


Simply copy & paste the code below into the Web IDE, then update the WIFI_NAME and WIFI_KEY variables and delete the onInit function that isn't for your platform (if you're using Espruino WiFi or a Pico with ESP8266).

For other hardware you'll have to consult the documentation and create your own onInit function.

Finally click the Send to Espruino button in the IDE.

var WIFI_NAME = "";
var WIFI_KEY = "";
var wifi;

// This serves up the webpage
function onPageRequest(req, res) {
  var a = url.parse(req.url, true);
  if (a.pathname=="/") {
    // handle the '/' (root) page...
    // If we had a POST, handle the data we're being givem
    if (req.method=="POST" && 
    // Otherwise write the main page. We're using
    // ES6 Template Literals here to make the HTML easy
    // to read.
    res.writeHead(200, {'Content-Type': 'text/html'});
  <form action="#" method="post">
    <label for="mytext">Some text to send:</label>
    <input type="text" id="mytext" name="mytext" value="Testing"/><br/>
    <label for="led1">LED1 (red):</label>
    <input type="checkbox" id="led1" name="led1" value="1"><br/>
    <label for="led2">LED2 (green):</label>
    <input type="checkbox" id="led2" name="led2" value="1"><br/>
  } else {
    // Page not found - return 404
    res.writeHead(404, {'Content-Type': 'text/plain'});
    res.end("404: Page "+a.pathname+" not found");

// This handles any received data from the POST request
function handlePOST(req) {
  var data = "";
  req.on('data', function(d) { data += d; });
  req.on('close', function() {
    // closed - now handle the url encoded data we got
    var postData = {};
    data.split("&").forEach(function(el) {
      var els = el.split("=");
      postData[els[0]] = decodeURIComponent(els[1]);
    // finally our data is in postData
    // do stuff with it!
    console.log("We got sent the text ", postData.mytext);
    digitalWrite(LED1, postData.led1);
    digitalWrite(LED2, postData.led2);

// This is called when we have an internet connection
function onConnected() {
  wifi.getIP(function(err, ip) {
    console.log("Connect to http://"+ip.ip);

// Initialisation for Espruino WiFi ONLY
function onInit() {
  wifi = require("EspruinoWiFi");
  wifi.connect(WIFI_NAME, { password : WIFI_KEY }, function(err) {
    if (err) {
      console.log("Connection error: "+err);

// Initialisation for Espruino Pico + ESP8266 ONLY
function onInit() {
  Serial1.setup(115200, { tx: B6, rx : B7 });
  wifi = require("ESP8266WiFi_0v25").connect(Serial1, function(err) {
    if (err) throw err;
    console.log("Connecting to WiFi");
    wifi.connect(WIFI_NAME, WIFI_KEY, function(err) {
      if (err) {
        console.log("Connection error: "+err);

// Comment this line out if you're planning on saving your code

A few seconds after the upload you should see a line like: Connect to

If you click on the URL, or copy/paste it into your browser, you should see something like this:

a form

You can then choose some options and click Submit, and the relevant LEDs will light.

Information about the code itself is in the comments, but for more information on forms check out the great MDN Article

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