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Create a config.json file in your project directory. First, use our guide to provision an SMS number and messaging profile, and create an API key. Then add those to the config file, along with your country code.

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{
    "API_KEY": "YOUR_API_KEY",
    "COUNTRY_CODE": "+1",
    "FROM_NUMBER": "YOUR_TELNYX_NUMBER" 
}

Server Initialization

First, import the config file and initialize the Telnyx library.

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const config = require('./config.json');
const telnyx = Telnyx(config.API_KEY);

Then create an express app that watches the templates directory with Nunjucks, a simple templating language, and parses form data.

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const app = express();
app.use(express.urlencoded());
app.set('views', `${__dirname}/templates`);

expressNunjucks(app, {
    watch: true,
    noCache: true,
});

Collect User Input

Create a simple HTML form, index.html, which collects the meeting date, time, customer name, and phone number. The full HTML source can be found in our GitHub repo, and we'll serve it at the root.

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app.get('/', (req, res) => {
    res.render('index');
});

Implement the SMS Notification

Create a function that sends an SMS message parameterized on the destination number and text.

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function sendReminder(to, message) {
    telnyx.messages.create({
        to: `${config.COUNTRY_CODE}${to}`,
        from: config.FROM_NUMBER,
        text: message 
    });
}

Parse User Input and Schedule the Message

Within the POST handler, parse the meeting time and compute how far into the future it is. We're using the moment Javascript library for this. Note that moment will use the current timezone for both datetime instances.

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app.post('/', (req, res) => {
    const meetingDatetime = moment(
        `${req.body.meeting_date} ${req.body.meeting_time}`,
        'YYYY-MM-DD hh:mm');
    const now = moment();

    const delta = moment.duration(meetingDatetime.diff(now));
    // ...
}

If the meeting is sooner than 3 hours, 5 minutes from now, return an error.

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if (delta < moment.duration({hours: 3, minutes: 5})) {
    res.render('index', {message: 'Can only schedule meetings at least 3 hours, 5 minutes in the future'});
} else {
    // ...
}

Remind the User

If the time is valid, compute when to send the reminder and schedule the function call. Note that we're using setTimeout here, but a production solution should make use of an asynchronus processing toolkit.

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const reminderDatetime = meetingDatetime.subtract(3, 'hours');
const message = `${req.body.customer_name}, you have a meeting scheduled for ${meetingDatetime}`;

setTimeout(() => {
    sendReminder(req.body.phone, message);
}, reminderDatetime.diff(now));

Finally, render the success template, success.html.

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res.render('success', {
    name: req.body.customer_name,
    meetingName: req.body.meeting_name,
    meetingDT: meetingDatetime,
    phone: req.body.phone
});

Start the Server

Start the Express app.

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const port = 3000;
app.listen(port, () => console.log(`App running on port ${port}`));

Running the Project

Simply run node scheduler.js at the command line.