Saving Data to Flash with DeviceScript Settings

DeviceScript Settings allow you to save values in flash memory so they can be retrieved after a reboot.

This is necessary because RAM is volatile. In almost any real-world (“production”) project, we need to permanently store certain data:

• A counter for how many times the machine has been powered on.
• The user’s preferred brightness setting.
• The last relay state to restore it when power returns.

In the classic Arduino world, we used the EEPROM library or, more recently on ESP32, Preferences.

In DeviceScript, we have a unified and much friendlier mechanism: the Settings package.

Reading and Writing Values

To use it, we need to import readSetting and writeSetting from @devicescript/settings.

Writing Data

import { writeSetting } from "@devicescript/settings"

// Save a number
await writeSetting("bright", 80)

// Save a string
await writeSetting("name", "Luis")

The call uses await because writing to flash is an asynchronous operation.

Reading Data

Here’s an important detail: What if the data doesn’t exist? (For example, the first time we power up the board). We can pass a default value to readSetting.

import { readSetting } from "@devicescript/settings"

// Read the value
const savedBrightness = (await readSetting<number>("bright")) ?? 50

console.log(`Retrieved value: ${savedBrightness}`) 

Example: Reboot Counter

The “Hello World” of persistence is counting how many times our device has started. This proves the data survives a power cycle.

import { readSetting, writeSetting } from "@devicescript/settings"
import { delay } from "@devicescript/core"

async function manageCounter() {
    console.log("Starting system...")

    // 1. Read the current value. If it doesn't exist, start at 0.
    let counter = (await readSetting<number>("boot_count")) ?? 0

    console.log(`This device has been rebooted ${counter} times.`)

    // 2. Increment and save for next time
    counter++
    await writeSetting("boot_count", counter)
    
    console.log("New value saved. Reboot me!")
}

manageCounter()

Saving Objects as JSON

The Settings service saves basic types. But what if we want to save our entire device configuration at once?

const config = {
    mode: "auto",
    thresholds: { min: 20, max: 30 },
    active: true
}

We can’t save a JS object directly. But we have an old friend to help us: JSON.

We convert the object to text (stringify) to save it, and convert it back to an object (parse) when reading.

import { readSetting, writeSetting } from "@devicescript/settings"

const CONFIG_KEY = "config"

// --- SAVE ---
async function saveConfig(cfg: any) {
    const text = JSON.stringify(cfg)
    await writeSetting(CONFIG_KEY, text)
    console.log("Configuration saved.")
}

// --- LOAD ---
async function loadConfig() {
    const text = (await readSetting<string>(CONFIG_KEY)) ?? ""
    
    if (!text) {
        // Return a default configuration if nothing is saved
        return { mode: "manual", thresholds: { min: 0, max: 100 } }
    }
    
    // Convert the text back to an object
    return JSON.parse(text + "")
}

Deleting Data

Sometimes we need a “Factory Reset” and erase everything. For that, the easiest way is to use the VS Code extension itself.

Run DeviceScript: Clear Device Settings... to clear the settings on the connected device.

Difference Between Settings and Secrets

An important distinction in DeviceScript:

• Settings: For your application data (colors, counters, preferences). They can be easily read and written from code.
• WiFi or MQTT Secrets: Go in .env.local, are not uploaded to Git, and are transferred to the device during deployment. Do not display them in the console.