Tips from Slaven

There is a pause in my forehand which disrupts the flow of my swing. I also have to try to hit the ball more ahead of me. Use the opposite hand to bring the racket slowly but continuously to start position at the back and then let it drop and come forward without flexing my arm, that is I need to stay as loose with arm as possible and let the power come from legs and pelvis and then torso.

Switching from Rollup to Esbuild for bundling frontend resources

npm node.js

I recently refactored my frontend build, switching from Rollup to Esbuild for bundling JavaScript and CSS. The change reduced the build time to less than half (from 21s to 10s). Below are a few things I learnt during this change:

Open-Source Web Development Tools

Thunder Client Rest Client for Testing APIs in VS Code
esbuild Bundle modules and scripts for better performance in browsers
LocaPing Traceroute From Multiple Locations. Enter your site's domain name and select a country to find out location and performance of the server hosting your domain to users visiting from that country.
iview Use to find out X and Y coordinates of any point in an image.
Image to Base64 Encode images to Base64

JavaScript Best Practices


Using Location API on anchor elements


Did you know that a HTML anchor element can be treated as a Location object? This means similar to how you can use window.location to read or write different parts of a URL, you can do the same with an anchor element. For example if you have a link like this:

<a id="myLink" href="https://mydomain/products.html#productName">test</a>

You can get the value of hash in this way:

    	const hash = document.getElementById('myLink').hash.substring(1);
    	// returns productName

You can use different properties of Location object on an anchor element and same as with window.location you can both read and write these properties. For more info see:

Fixing TypeScript error property does not exist on type EventTarget


When working with event listeners in TypeScript one often runs into error that a particular property does not exist on type EventTarget. While it's relatively easy to fix this error using type "any" or by typecasting the event target using "as", none of these solutions are optimal since they simply disable TypeScript's type checking, which is what we are using TypeScript for in the first place!

The better way to fix this error is to use JavaScript's instanceof operator which you can read about at:

Example of code that throws error:

    	document.querySelector('p').addEventListener('click', (event) => {


Property 'textContent' does not exist on type 'EventTarget'.


    	document.querySelector('p').addEventListener('click', (event) => {
    	if ( instanceof Element) {

Closing an open port via Mac's terminal


Use below command in terminal to get a list of all open ports:

netstat -an | grep LISTEN

Find the process ID (PID) of the port you wish to close. You may need to use sudo.

lsof -i :[portNumber]

Then use the following command to kill the process listening on your port. You may need to use sudo with kill -9 parameter.

kill PID

Deploying a static HTML page and a serverless function (Node.js) live via Vercel

vercel node.js

In this example you will create a static HTML page that calls an api (Node.js serverless function) which responds by returning the word "Hello World" and displaying it in the browser. You can see a deployed version at:

We will deploy and host both the HTML page and the Node.js api on Vercel using Vercel's cli, so you should register for a free account at if you don't already have one and install vercel's command line via:

    	npm install -g pnpm
    	pnpm i -g vercel

  1. Run the following in terminal to create file and folder structure for "test" project:
        	mkdir test
        	cd test
        	mkdir public api
        	cd api
        	touch index.js
        	cd ../public
        	touch index.html
        	cd ..
  2. Open index.html in your editor and paste the following snippet there:
        	<!DOCTYPE html>
        	<html lang="en">
        	        <meta charset="utf-8" />
        	        <title>Hello World</title>
        	        <meta name="viewport" content="width=device-width, initial-scale=1" />
        	        <p id="test"></p>
        	          .then((response) => response.text())
        	          .then((text) => {
        	            document.getElementById('test').innerHTML = text;
  3. Open index.js in your editor and paste the following snippet there:
        	export default function handler(req, res) {
        	    res.setHeader('Content-Type', 'text/plain')
        	    res.write('Hello World')
  4. In cli/terminal run:
    vercel dev
    and select default answers to all questions. Vercel cli will create the test project under your existing Vercel account and start a local server at: http://localhost:3000/ where you can see your index.html and your api can be reached at: http://localhost:3000/api/. If everything is working properly, you should see a "Hello World" message in your browser.
  5. To deploy your project to server for preview purposes run in terminal:
    vercel deploy
    And if you are happy with result and want to deploy it to production run:
    vercel --prod
    The preview and production URLs are available in your project on under "Deployment" tab.

Responsive images that do not scale up beyond their intrinsic size

css responsive

Usually all you need to make an image resize based on size of screen is to add one simple CSS rule:

img {
    	  width: 100%;

However if the screen resolution is higher than width of your image, this would result in a blurred image as there is simply not enough data in image to render it at higher resolutions. In such cases it might be more desirable to keep the image responsive, but not allow it to get larger than it's actual size. This can be achieved by the following CSS rule:

img {
    	  width: auto;
    	  max-width: 100%;

Deploy to Vercel only when a specific file or folder in repository is changed

vercel github

When you install Vercel application on GitHub and give it access to your repository, GitHub will trigger a deployment on Vercel every time there is a new commit in your main branch, however if your API on Vercel only needs to be updated when a certain file or folder is changed, these deployments are unnecessary. You can avoid unnecessary deployments to Vercel using GitHub Actions as described here:

Another advantage of using GitHub Actions with Vercel is that you can uninstall Vercel application from GitHub as Vercel no longer needs access to your GitHub repository. You simply need to create a token on Vercel and store it along with your Vercel Org and Project IDs (found in .vercel/project.json in root of your project) in secrets on Github at

vercel secrets on GitHub

Disabling preview deployments in Vercel


If you don't want Vercel to do preview deployments for other branches of your repository you can disable preview deployments by going to your project's settings > git > Ignored Build Step and add the following command:

if [ "$VERCEL_ENV" == "production" ]; then exit 1; else exit 0; fi

This is probably the easiest way. Another way would be to add a vercel.json to all branches and set "deploymentEnabled" to false for any branches that should not trigger deployment, like below:

    	  "git": {
    	    "deploymentEnabled": {
    	      "gh-pages": false

More info: