Category Archives: JavaScript

JavaScript Basic Spread and Rest (…) usage

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The Spread and Rest operators i.e. the three dots (…) can be used to make code cleaner and more concise.

Difference between Spread and Rest

Spread: Works on elements on the right side of the = operator, and breaks them out into individual elements.

Rest: Works on the left hand side of the = operator, and compresses them into an array.

Using Spread to Iterate over Arrays

Spread works on iterables like strings, arrays, maps and sets.

The spread operator operates similar to taking all the elements out of an array and operating on them or writing them to a new array. Say for instance we have an array of computers and we want to log each element to the console.

const computersA = ['Acer', 'Apple', 'ASUS']

We can log each element by running

console.log(computersA[0], computersA[1], computersA[2])

Or we can use the spread operator

console.log(...computersA)

The output is the same.

Joining Arrays

We can also use the spread operator to join two arrays together. Say we have two arrays

const computersA = ['Acer', 'Apple', 'ASUS']
const computersB = ['HP', 'Dell', 'Lenovo']

And we want to concatenate them together. We can do that simply by

const computerAll = [...computersA, ...computersB]

Rest Example

Rest is simply the opposite of spread. Spread take an item like an array and expands it out into elements we can use. Rest takes elements and packs them into an array. This can be extremely helpful if we want to pass in an unknown amount of elements into a function for processing.

const computersA = ['Acer', 'Apple', 'ASUS']
function writeToLog (...arr) {
  for (const element of arr) {
    console.log(element)
  }
}

Now we can call the function with as many elements in the array and they will all get logged to the console.

writeToLog('Razer', 'Alienware', 'Legion')

We could also use both the Spread and Rest functions

const gamingLaptops = ['Razer', 'Alienware', 'Legion']
writeToLog(...gamingLaptops)

Now as we add more laptops to the gamingLaptops array, the function will automatically process the line and write to console.

https://www.freecodecamp.org/news/three-dots-operator-in-javascript/

Send an Email with Node.JS

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In this post, we will be using Node.JS and the nodemailer library to send email. We need to have an email account with an email provider to send email. Gmail or some other email provider should work.

Prerequisites

First lets install some tools

sudo apt install nodejs npm

Now lets install nodemailer

npm install nodemailer

Writing the Code to Send Email

Now that we have nodemailer installed, we can write or copy our code. Create a file called maill.js and make it look similar to the following.

// We can pass in the email text as an argument
const emailText = process.argv.slice(2);
// Or we can just have it as a variable
// const emailText = "NodeJS test email message."
console.log("args " + args)

const nodemailer = require("nodemailer");

const transporter = nodemailer.createTransport({
  host: "mail.emailserver.com",
  port: 465,    //  If your email server does not support TLS, change to 587
  secure: true, // If you are using port 587, change to false.  Upgrade later with STARTTLS
  auth: {
    user: "smtpuser@emailserver.com",
    pass: "notpassword)",
  },
});

const mailOptions = {
  from: 'user@emailserver.com',
  to: "touser@email.com",
  subject: 'Test Email using NodeJS',
  text: `${emailText}`
};

transporter.sendMail(mailOptions, function(error, info){
  if (error) {
    console.log(error);
  } else {
    console.log('Email sent: ' + info.response);
  }
});

Update the following variables

  • host: to your host email server
  • user: to the email user that is sending email. It should have an account on the email server
  • pass: password for your email user that is sending the email
  • from: email address that is sending the email
  • to: email account(s) you are sending email to
  • subject: subject of your email

Now we can proceed to send email

Sending Email

We can now run the code by saving our file and running it directly with NodeJS

nodejs ./mail.js "This is the body text for the email"

Hit Return and look for the email. If something went wrong, it should throw an error.

You can change the emailText variable if you would rather have the message body inside the code.

Code Explanation and Notes

A little explanation on the code.

The second line “const emailText = process.argv.slice(2);” is used to pass in a command line argument to use as the text for the body of the email. You can delete the line and uncomment line 4 if you would rather use a variable inside the code.

Your email server should support using SSL/TLS on port 465. If it does not, you may need to use STARTTLS which uses port 587, and then set secure to false. STARTTLS should upgrade the connection to be encrypted. But it’s opportunistic. You can read more about STARTTLS, SSL/TLS here https://mailtrap.io/blog/starttls-ssl-tls/

You can change the “to: ” in the mailOptions object to an array of email addresses to send the email to multiple people at once. 

to: ["email1@email.com", "email2@email.com", "etc"],

JavaScript check if a string matches any element in an Array

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In the following code we will be checking a string and check if any of the words in the string match some or any elements in an array.

We can imagine that our “stringToCheck” variable is an email or message response. We want to know if it contains a mention to afternoon, tomorrow, or evening. Presumably so we can automate something. Note that the matches are case sensitive.

// Check if any text in a string matches an element in an array

const stringToCheck = "Let's grab lunch tomorrow";
const arrayToCompareTo =["afternoon", "tomorrow", "evening"];

// We are checking to see if our string "stringToCheck" 
// Has any of the words in "arrayToCompareTo".
// If it does, then the result is true.  Otherwise false.
const resultsOfCompare = arrayToCompareTo.some(checkVariable => stringToCheck.includes(checkVariable));

if (resultsOfCompare == true){
    console.log(stringToCheck + " Contains a value in our Array " + arrayToCompareTo);
} else {
    console.log(stringToCheck + " Does NOT contain a value in our Array " + arrayToCompareTo);
}

More examples and ways to do it are available at the following link.

https://stackoverflow.com/questions/37428338/check-if-a-string-contains-any-element-of-an-array-in-javascript

Simple JavaScript Object – Code Example

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Below is a code example for creating a basic object and using a function to calculate the fuel economy.

// New object Car
const car = {
    make: 'Honda',
    model: 'Civic',
    topSpeed: 100,
    tankCapacity: 10,
    range: 300,
    MPG: function() {
        this.mpg = this.range / this.tankCapacity;
        return this.mpg
    }
}

car.MPG();  // We need to call this to calculate the MPG, otherwise we get undefined

console.log(`My car is a ${car.make + " " + car.model }, can go ${car.topSpeed}/MPH, and gets ${car.mpg}/MPG `)

// Alternatively we can call the function car.MPG() directly.  
// This keeps us from having to run the function before logging.
console.log(`My car is a ${car.make + " " + car.model }, can go ${car.topSpeed}/MPH, and gets ${car.MPG()}/MPG `)