node js is single threaded code example

Example 1: javascript is single threaded

JavaScript is a single-threaded language, which means it has 
only one call stack that is used to execute the program. The 
call stack is the same as the stack data structure that you might 
read in Data structures.

Example 2: how to make use of nodejs single thread to read files and attach data

var mailer = require('nodemailer');
mailer.SMTP = {
    host: 'host.com', 
    port:587,
    use_authentication: true, 
    user: '[email protected]', 
    pass: 'xxxxxx'
};

Then read a file and send an email :

fs.readFile("./attachment.txt", function (err, data) {

    mailer.send_mail({       
        sender: '[email protected]',
        to: '[email protected]',
        subject: 'Attachment!',
        body: 'mail content...',
        attachments: [{'filename': 'attachment.txt', 'content': data}]
    }), function(err, success) {
        if (err) {
            // Handle error
        }

    }
});