http://thejackalofjavascript.com/raspberry-pi-node-js-led-em

/**
  * Inspired by: http://thejackalofjavascript.com/raspberry-pi-node-js-led-emit-morse-code/
  */
// Example: node morse.js sos

// Uncomment the following to test script when event loop spins forever
// const spinTestExecFunction = process.nextTick

// Uncomment the following to test script when event loop is saturated
// const spinTestExecFunction = setImmediate

const onoff = require("onoff");
const Q = require("q");
const gapDurationMillis = 10; /* Smallest unit of time to wait */
const postDeactivateGaps = 5; /* How long to wait after using led */
const codes = { /* Morse codes */
        "." : {enableLed:true, gaps:10}, // dot
        "_" : {enableLed:true, gaps:40}, // dash
        "|" : {enableLed:false, gaps:20}, // letter end
        ":" : {enableLed:false, gaps:0} // word separator
    };
const pattern = { /* Conversion from sourceLetter to morseCodes */
        "a": "._|",
        "b": "_...|",
        "c": "_._.|",
        "d": "_..|",
        "e": ".|",
        "f": ".._.|",
        "g": "__.|",
        "h": "....|",
        "i": "..|",
        "j": ".___|",
        "k": "_._|",
        "l": "._..|",
        "m": "__|",
        "n": "_.|",
        "o": "___|",
        "p": ".__.|",
        "q": "__._|",
        "r": "._.|",
        "s": "...|",
        "t": "_|",
        "u": ".._|",
        "v": "..._|",
        "w": ".__|",
        "x": "_.._|",
        "y": "_.__|",
        "z": "__..|",
        "1": ".____|",
        "2": "..___|",
        "3": "...__|",
        "4": "...._|",
        "5": ".....|",
        "6": "_....|",
        "7": "__...|",
        "8": "___..|",
        "9": "____.|",
        "0": "_____|",
        ".": "._._._|",
        ",": "__..__|",
        "?": "..__..|",
        "/": "_.._.|",
        "@": ".__._.|",
        " ": ":"
    };

var main = function (text) {
        var led = new onoff.Gpio(17, "out");
        emitTextAsMorseCodeAsPromise(led, text)
            .done(function (o) {
                console.info("DONE!");
                process.exit(0);
            });
    },
    emitTextAsMorseCodeAsPromise = function (led, text) {
        var promise = Q(),
            normalizedText = text.toLowerCase()
                .replace(/[^a-z0-9\.,\?/@]+/g, " ");
        console.info("Text to morse code: [" + normalizedText + "]");
        normalizedText.split("")
            .forEach(function (sourceLetter) {
                var morseCodes = pattern[sourceLetter];
                promise = promise.then(function () {
                    console.log("morseCode: [" + sourceLetter + "] -> [" + morseCodes +"]");
                });
                morseCodes.split("")
                    .forEach(function (morseCode) {
                        promise = promise.then(function () {
                            return emitMorseCodeAsPromise(led, morseCode);
                        });
                    });
            });
        return promise;
    },
    emitMorseCodeAsPromise = function (led, morseCode) {
        return Q({led:led, morseCode:morseCode})
            .then(function (bucket) {
                var code = codes[bucket.morseCode];
                if (!code) {
                    throw new Error("Unknown code: ["+bucket.morseCode+"]");
                }
                bucket.code = code;
                console.log("emitting: [" + bucket.morseCode +"]");
                if (bucket.code.enableLed) { // activate
                    bucket.led.writeSync(1);
                }
                return Q(bucket).delay(getGapDelay(bucket.code.gaps));
            })
            .then(function (bucket) {
                if (bucket.code.enableLed) { // deactivate
                    bucket.led.writeSync(0);
                    return Q(bucket).delay(getGapDelay(postDeactivateGaps));
                }
                return bucket;
            });
    },
    getGapDelay = function (gaps) {
        return gapDurationMillis * gaps;
    };

// Add duration of script to console messages
(function (con) {
    var functions = {}, key, startTime = process.hrtime(),levelLabel = { "log" : "DEBUG", "info" : "INFO", "warn" : "WARN", "error" : "ERROR", "trace" : "TRACE" },getTime = function () {var runningTime = process.hrtime(startTime);return "" + runningTime[0] + "." + "0".repeat(9 - Math.ceil(Math.log10(runningTime[1]))) + runningTime[1];/* return new Date().toISOString().toString(); */};
    for (key in con) {
        if (typeof(con[key]) != "function") { continue; }
        switch (key) { case "log": case "info": case "warn": case "error": case "trace":
            functions[key] = con[key]; // original function
            con[key] = (function(name) {return function () {Array.prototype.unshift.apply(arguments,["["+getTime()+"]","["+levelLabel[name]+"]"]);functions[name].apply(con, arguments);}})(key)
            break;
        default: break;
    }}
})(console);

// Start our app
process.nextTick(function () {
    main((process.argv[2] ? process.argv[2] : ""));
});

(function spinForever () {
    if (typeof spinTestExecFunction == "undefined") { return; }
    process.stdout.write(".");
    spinTestExecFunction(spinForever);
})();