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Get day of week

Get the day of the week for a given day

function getWeekDay(forDate) {
    const days = [
        "Sunday",
        "Monday",
        "Tuesday",
        "Wednesday",
        "Thursday",
        "Friday",
        "Saturday"
    ];

    return days[new Date(forDate).getDay()];
}

console.log(getWeekDay("2026-02-20"));  // get the day for a given date
console.log(getWeekDay(new Date()));  // get todays day

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Return a number within a range

function clamp(num, min, max) {
    return Math.min(Math.max(num, min), max);
}

console.log(clamp(10, 0, 5)); // outside range. closest value is 5
console.log(clamp(-10, 0, 5)); // outside range. closest value is 0
console.log(clamp(3, 0, 5)); // in range. Just return 3

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Ordinal descriptor for day

Get the ordinal descriptor suffix for the day of a month

function getDaySuffix(day) {
    // Validate input
    if (!Number.isInteger(day) || day < 1 || day > 31) {
        throw new Error("Day must be an integer between 1 and 31.");
    }

    // Handle special cases for 11th, 12th, 13th
    if (day % 100 >= 11 && day % 100 <= 13) {
        return `${day}th`;
    }

    // Determine suffix based on last digit
    switch (day % 10) {
        case 1: return `${day}st`;
        case 2: return `${day}nd`;
        case 3: return `${day}rd`;
        default: return `${day}th`;
    }
}

// Example usage:
console.log(getDaySuffix(1));   // "1st"
console.log(getDaySuffix(2));   // "2nd"
console.log(getDaySuffix(3));   // "3rd"
console.log(getDaySuffix(4));   // "4th"

const d = new Date(); // get the current day
const day = d.getDate();  // gets day of the month
console.log(getDaySuffix(day));   // Suffix for today

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Get a random UUID

import crypto from 'crypto';

// Example usage
console.log("Generated UUID:", crypto.randomUUID());

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Read environment variables

Read environment variables from .env file, if environment is not set at the OS level.

must use node --env-file=.env xxx.mjs

console.log(`Reading from Environment variables: 
    ${process.env.GREETING}
    ${process.env.SECRET_PSW}
    ${process.env.NODE_ENV}
`);

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Asynchronously reading a file with fs/promise

Use fs/promises as this is the modern implementation

import fsPromises from 'fs/promises';

async function readFileExample() {
    try {
        const data = await fsPromises.readFile('settings.json', 'utf8');
        return data;
    } catch (error) {
        return JSON.stringify({ error: error });
    }
}

readFileExample()
    .then((data) => {
        console.table(data);
    })
    .catch((err) => {
        console.log(err);
    });

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Asynchronously reading multiple files

Wrap multiple fs async reads in a promise.

import fsPromise from 'fs/promise';

async function readMultipleFiles() {
    const filesToRead = ['settings.json', 'new.txt']
    try {
        const results = await Promise.all(filesToRead.map((file) => fsPromises.readFile(file, 'utf8')))
        return results;
  } catch (err) {
        return JSON.stringify({ error: err });
  }
}

readMultipleFiles()
    .then((data) => {
        data.forEach(res => console.table(JSON.parse(res)));
    })
    .catch((err) => {
        console.log(err);
    });

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Get someone’s age

Get someone’s age from their birthdate

function getAge(birthDateString) {
    let today = new Date();
    let birthDate = new Date(birthDateString);

    // Difference in milliseconds
    const diffMs = today.getTime() - birthDate.getTime();

    // Convert to other units
    const diffSeconds = Math.trunc(diffMs / 1000);
    const diffMinutes = Math.trunc(diffSeconds / 60);
    const diffHours = Math.trunc(diffMinutes / 60);
    const diffDays = Math.trunc(diffHours / 24);
    const diffYears = Math.trunc(diffDays / 365);

    return {
        years: diffYears,
        days: diffDays,
        hours: diffHours,
        minutes: diffMinutes,
        seconds: diffSeconds,
        milliseconds: diffMs
    };
}

console.log(getAge("1998-08-13")); // get age

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Events and event emitters

import EventEmitter from 'events';
const emitter = new EventEmitter();

emitter.on('greet', (name) => {
    console.log(`Hello, ${name}!`)
});

// put the event trigger in a timer to make it run after other examples do
setTimeout(() => emitter.emit('greet', 'Fred'), 14000);

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Serialising and deserialising an object to and from a file

Ideal for reading and writing settings to a configuration file.

Notice the JSON.stringify option in fs.writefile(). The , null, 2 option will indent and format the output for the file, rather than it all being on a single line.

// create setting object
let mySettings = {
    user: "baggz",
    firstName: "Fred",
    surname: "Flintstone",
    darkMode: true,
    age: 57
}

// serialise setting object and write to file
fs.writeFile('settings.json', JSON.stringify(mySettings, null, 2), (err) => {   
    if (err) return console.error('Error writing file:', err);
    logger('Write object to a file');
    console.log('Settings written successfully to settings.json.');
});

// Read the settings file, then deserialise it into a new object
let mySettings2 = {};
// Read a file (asynchronous)
fs.readFile('settings.json', 'utf8', (err, data) => {
    if (err) return console.error('Error reading file:', err);
    mySettings2 = JSON.parse(data);
    logger('Reading file contents into an object');
    console.log('Setting file contents read into object');
    console.log('Test object read: ' + mySettings2.age);
    console.log();
});

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Itterate object properties

Itterate through all properties of an object

// create an object
const fakeBody = {
    jigery: "pokery",
    title: "my title",
    age: 180,
    badData: "<script>alert('KaKow');</script>"
};

// Get all the keys for the object, then test the values if unusafe
for (const [key, value] of Object.entries(fakeBody)) {
    // safe = false, unsafe = true
    console.log(fakeBody[key], /[$&+,:;=?@#|'<>.^*()%!-]/g.test(fakeBody[key]));
}

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Hash strings

Hash a string to compare if it has changed

function hashRequest(thing) {
    const content = JSON.stringify(thing) || '';
    return crypto.createHash('sha256').update(content).digest('hex');
}

let changingString = "cat";
let firstHash = hashRequest(changingString);
changingString = "dog";
let secondHash = hashRequest(changingString);

console.log(firstHash);
console.log(secondHash); // Different to firstHash. Has changed

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Bubble sort

Doing a bubble sort - compare-swap-repeat

const sortArr = [12, 1, 3, 3, 6, 13, 8, 5, 3, 5];

const bubbleSort = (arr) => {
    let swapped;

    do {
        swapped = false;
        for (let i = 0; i < arr.length - 1; i++) {
            if (arr[i] > arr[i + 1]) {
                let temp = arr[i];
                arr[i] = arr[i + 1];
                arr[i + 1] = temp;
                swapped = true;
            }
        }
    } while (swapped);

    return arr;
};

console.log(sortArr); // pre-sort
console.log(bubbleSort(sortArr)); // post-sort

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Capitalise first letter of words

Capitalise first letter of each word, with the remaining letters lower case

// capitalise the first letter of each word, with the rest lower case
const haiku = "My code fAiLs I do not knoW why My code works I do not know wHy.";
console.log(haiku);

const capped = haiku
    .toLowerCase()
    .split(' ')
    .map(word => word[0].toUpperCase() + word.slice(1))
    .join(' ');

console.log(capped);

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Flatten a multi-dimensional array

Get the depth of a multi-dimensional array, flatten it, then convert to string

console.time("arrDep1");
const getArrayDepth = value => Array.isArray(value) ?
    1 + Math.max(0, ...value.map(getArrayDepth)) :
    0;

const a = [1, 2, [1, [1, 2, 3, [1, [1, 2, 3, [1]]]], 3], 3, 4];
console.log(a);
const depth = getArrayDepth(a);
console.log('Array depth is', depth);
console.log('Flattened as string is', a.flat(depth).toString());
console.timeEnd("arrDep1");

console.time("arrDep2");
//console.log('Flattened2 as string is', a.flat(infinity).toString());
console.timeEnd("arrDep2");

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Chart.js

Use chart.js to create chart images for your data.

import {CategoryScale, Chart, LinearScale, LineController, LineElement, PointElement} from 'chart.js';
import {Canvas} from 'skia-canvas';
import fsp from 'node:fs/promises';

Chart.register([
  CategoryScale,
  LineController,
  LineElement,
  LinearScale,
  PointElement
]);

const canvas = new Canvas(400, 300);
const chart = new Chart(
  canvas, // TypeScript needs "as any" here
  {
    type: 'line',
    data: {
      labels: ['Red', 'Blue', 'Yellow', 'Green', 'Purple', 'Orange'],
      datasets: [{
        label: '# of Votes',
        data: [12, 19, 3, 5, 2, 3],
        borderColor: 'red'
      }]
    }
  }
);
const pngBuffer = await canvas.toBuffer('png', {matte: 'white'});
await fsp.writeFile('output.png', pngBuffer);
chart.destroy();

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Temperature conversion

Celcius to Fahrenheit and Fahrenheit to Celcius

const celciusToFahrenheit = celcius => Math.round(((celcius * 9/5) + 32) * 10) / 10; // round to 1 decimal place
const FahrenheitToCelcius = fahrenheit => Math.round(((fahrenheit -32) / (9/5)) * 10) / 10; // round to 1 decimal place

console.log(celciusToFahrenheit(37.8));
console.log(FahrenheitToCelcius(100));

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Return unique array elements

Using Set to get the unique array elements

const repeats = ["cat", "dog", "cat", "dog", "cat", "dog", "dog", "dog"];
const unique = arr => [...new Set(arr)];
console.log(unique(repeats));

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Check if an Object is empty

Object key length is zero

const isEmpty = obj => Object.keys(obj).length === 0;

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Generate a random HEX colour

Using Math.Random()

const randomColour = () => `#${ Math.floor( Math.random() * 0xFFFFFF )
    .toString(16)
    .padStart(6, '0')}`;

console.log(randomColour());

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Debounce a function

Pause before executing, and reset pause if call again in that initial pause. Reduces the chance that double calls are processed. (Mainly seen in client code for things like search as you type or auto-complete text)

// Debounce function
function debounce(func, delay) {
    let timeout;
    return function (...args) {
        clearTimeout(timeout);
        timeout = setTimeout(() => {
            func.apply(this, args);
        }, delay);
    };
}

// Function to be debounced
function search(query) {
    console.log('Searching for:', query);
}

// Create a debounced version of the search function
const dSearch = debounce(search, 1000);

// Simulate typing with multiple calls to the debounced function
dSearch('Hello');
dSearch('Hello, ');
dSearch('Hello, World!');  // Only this call will trigger after 1000ms

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Copy to clipboard

Copy text to the clipboard (client code only)

<input type="button" value="Copy to clipboard" 
    onclick='copyToClipboard("I am text to copy")'>

const copyToClipboard = text => navigator.clipboard.writeText(text);

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Load version number from package.json

The package.json is just a JSON file, so we can load it and process it like any other JSON file. This way we can use the version number here to display in an app. You must include the with {type:'json'} option when importing JSON.

import pkg from './package.json' with { type: 'json' };
console.log(pkg.version);

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AU Phone number match

// match phone number format (AUS)
let ausPhoneNumbers = [
    "8217 5530",
    "82175530",
    "(08) 8217 5530",
    "+61 413 332 333",
    "0413332333",
    "08 8217 5530"
];

ausPhoneNumbers.forEach(num => {
    console.log(num, num.match(/^(\s\+?\(61\)|\(\+?61\)|\+?61|\(0[1-9]\)|0[1-9])?( ?-?[0-9]){7,9}$/gm));
});

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Email validity

let emails = [
    "austin_powers@hmss.gov.co",
    "doctor.evil@secret.lair.com",
    "ron.burgandy@news.com",
    "bad_actor@@oonka-woonka",
    "matt.p.8675309@gmail.com",
    "elbo.pm@dick.wad.au",
    "please-explain@right.now.au"
];

// test email validity
emails.forEach(email => {
    console.log(email, /\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z0-9]{2,}$/.test(email));
});

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Password validity check

let password = "Abcd123!";

checkPswComplexity(password);

function checkPswComplexity(password) {
    let hasUpperCase = /[A-Z]/.test(password);  // upper case
    let hasLowerCase = /[a-z]/.test(password);  // lower case
    let hasNumbers = /\d/.test(password);  // has numbers
    let hasNonalphas = /\W/.test(password);  // has symbols
    if (password.length >= 8 && hasUpperCase && hasLowerCase && hasNumbers && hasNonalphas) { // check all true
        console.log("Good password");
    } else {
        console.log("Bad password");
    }
}

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Throttling

When you only want a function to run once per time period, regardless of how many times it is called.

// setup throttle function
function throttle(fn, delay) {
  let lastCall = 0;

  return function (...args) {
    const now = Date.now();
    if (now - lastCall >= delay) {
      lastCall = now;
      fn.apply(this, args);
    } else {
        console.log('Throttle call not run');
    }
  };
}

// setup function we only want to run periodically
function cat(sound) {
    console.log('Cat goes ' + sound);
    return;
};

// connect function to throttle to throttle test, and pass in time to throttle
const throt = throttle(cat,2000);


// call throttled fuction 3 times - pass param for throttle function
throt('woof'); // runs the first time
throt('tweet'); // doesn't run as within 2 seconds of first call
throt('Meow'); // doesn't run as within 2 seconds of first call

// wait 5 seconds
setTimeout(() => {
    throt('Mooooo')  // runs as past 2 second throttle time
},5000);

Cat goes woof
Throttle call not run
Throttle call not run
Cat goes Mooooo

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Express middleware parameter wrapper

Pass optional parameters to custom express middleware. eg app.use(customMiddleware(customParam));

// wrapper pattern to pass a variable in before the middleware is called. 
export const customMiddleware = function (action = "blah") {
    console.log(`Custom middleware: Activated - Mode: ${action}`);

    return (req, res, next) => {
        if (req.body != undefined) {
            switch (action.toLowerCase()) {
                // do something
                case "blah":
                    return res.setHeader('Content-Type', 'application/json').status(400).json({ message: something, status: "xxx" });
                    break;
                // if a bogus option was passed, show an error
                default:
                    res.status(500);
                    console.log(`Middleware (Mode: ${action}) You have NOT SELECTED A VALID OPTION - no action taken !!!`);
                    res.setHeader('Content-Type', 'application/json').status(500).json(`{message: middleware triggered, but using invalid option '${action}' - No action taken }`);
                    return;
                    break;
            }
        }
    }
    next();
}

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