# MQTT JS function output format
**URL:** https://discourse.nodered.org/t/mqtt-js-function-output-format/30183
**Category:** General
**Created:** [16 July 2020 08:38 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183 "2020-07-16T08:38:47Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@pautorras](https://discourse.nodered.org/u/pautorras)
#### Post date: [16 July 2020 08:38 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/1 "2020-07-16T08:38:47Z")
Hi,
I'm communicating NR with an ESP8266 with MQTT.
In dashboard, using a switch it works perfect. The switch output contains "on" or "off" and it works perfect.
I would like to use an MQTT output, with the output of a function. The function turns on or off a water valve depending on a time shedule.
¿Wich format needs the function output to "match" with the MQTT out?
PD- I have searched in the forum, but I hav'nt find it.
Thanks!
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### Author:  [@knolleary](https://discourse.nodered.org/u/knolleary)
#### Post date: [16 July 2020 08:51 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/2 "2020-07-16T08:51:04Z")
Hi @pautorras
the MQTT Out node will publish whatever value you pass it in `msg.payload`.
So if you want to publish the value `"on"` then that is what you should set `msg.payload` to.
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### Author:  [@dynamicdave](https://discourse.nodered.org/u/dynamicdave)
#### Post date: [16 July 2020 09:00 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/3 "2020-07-16T09:00:24Z")
What firmware are you using in the ESP8266 ??
e.g. ESP-Easy, Tasmota, ESP-Home, etc...
How is the water valve connected to the ESP8266 ??
By a relay on a GPIO pin ??
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### Author:  [@pautorras](https://discourse.nodered.org/u/pautorras)
#### Post date: [16 July 2020 14:35 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/4 "2020-07-16T14:35:49Z")
I'm programming ESP8266 with C++ using Arduino IDE
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### Author:  [@dynamicdave](https://discourse.nodered.org/u/dynamicdave)
#### Post date: [16 July 2020 16:18 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/5 "2020-07-16T16:18:12Z")
I'll have to leave that (to others on the forum) as C++ is not my field.
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### Author:  [@molesworth](https://discourse.nodered.org/u/molesworth)
#### Post date: [16 July 2020 17:08 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/6 "2020-07-16T17:08:48Z")
I'm doing something similar, using @knolleary's "PubSubClient" library, but I would expect other libs to work in a similar way. As an example of how to do it, here's my setup for an MQTT out node which sends a regular "tick" to any ESP8266 devices which need to keep an accurate time.
The message is generated by a simple Inject node sending a timestamp every 15 minutes, but as mentioned already, whatever you pass in as the message payload will be sent.
The code in the ESP8266 simply subscribes to "sys/tick" to receive the messages.
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### Author:  [@krambriw](https://discourse.nodered.org/u/krambriw)
#### Post date: [16 July 2020 18:20 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/7 "2020-07-16T18:20:18Z")
You can also simply send specific strings from the MQTT out node in Node-RED to your esp devices
In my esp32 I have the following C code that receives MQTT messages and "decode" them. Very simple but effective solution
```auto
// MQTT data callback
void mqtt_data_callback(mqtt_client *client, mqtt_event_data_t *event_data)
{
char cmd_string[64];
//printf("DATA=%.*s\r\n", event_data->data_length, event_data->data);
sprintf(cmd_string, "%.*s\r\n", event_data->data_length, event_data->data);
if (strstr(cmd_string, "init_task") != NULL) {
printf("\n\n\r");
printf("%s", cmd_string);
vTaskDelete( xHandle );
counter = 0;
vTaskDelay(1000 / portTICK_RATE_MS);
xTaskCreate(&read_temp, "read_temp_task", 10000, client, 5, &xHandle);
}
if (strstr(cmd_string, "hello") != NULL) {
mqtt_publish(client, "/hello", "hello to you too", 16, 0, 0);
}
}
```
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### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [14 September 2020 18:20 UTC](https://discourse.nodered.org/t/mqtt-js-function-output-format/30183/8 "2020-09-14T18:20:25Z")
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