This sample demonstrates how to run your JavaScript application as performing some action in response to an event, input or stimulus. Since Sming framework itself has an event-driven architecture such JavaScript applications will be able to use all the advantages that Sming has in terms of CPU, RAM and power usage.

JavaScript Code

Similar to Sming this sample calls the init JavaScript function. And in this function we register the events that we are interested in. As shown below.

 * This is a function that will be called once.
function init() {
        x = 0;
        print('Init: X=' + x);

        // This is how we register an event listener in JavaScript
        addEventListener("EVENT_TEMP", function(event) {
                // An event has a name and multiple params
                // the params have string keys and string values
                print('Event name: ' + event.name + ', value: ' + event.params['temp']);

        // ...

The addEventListener mimics the browser addEventListener function. It accepts two parameters - a unique event name and a callable function. Similar to the browser function you can add multiple callable functions to one event.

C/C++ Code

The addEventListener function is not present in the standard JerryScript VM. In this sample we register it as a built-in JavaScript function. Excerpt from the application.cpp file:

void startJsvm()
         * This is how we register a new function in JavaScript
         * that will communicate directly with our C/C++ code.
        jsVm.registerFunction("addEventListener", addEventListener);

        // ...

The actual implementation of the addEventListener C++ function is in the vm_functions.cpp file. There you will find also the triggerEvent function which is available only in the C/C++ code. The latter is used to trigger events from the C/C++ code inside the JavaScript application:

JsEventData params;
triggerEvent("EVENT_TEMP", params);

The code above simulates a temperature sensor sending the temperature in Celsius (C).


SoC support

  • esp32

  • esp32c2

  • esp32c3

  • esp32s2

  • esp32s3

  • esp8266

  • host

  • rp2040