JavaScript vs TypeScript - I built the same crypto tracker with both

If you are building a web application today, there are two heavyweights competing for your attention. In the red corner, we have JavaScript—the king of the web; and in the blue corner, we have TypeScript—the challenger from Microsoft.

Both tools achieve the same fundamental goal: they make things happen in a browser. But there is a world of difference in the developer experience. No matter which one you choose, the other one automatically becomes your arch-nemesis. Because you don’t choose anything but the absolute best technology out there.

To figure out which one is best, I built the exact same Real-Time Crypto Tracker with both JavaScript and TypeScript.

In this post, we are going to dive into a detailed side-by-side comparison of the features, tooling, ecosystem, performance, and of course, the code! By the end of this post, you will know exactly which one fits best in your ideology.

But this isn't a line-by-line coding tutorial. If you want to learn how to build these apps from scratch, subscribe to my free newsletter.

Let’s start by comparing the setup and the "Barrier to Entry."

Setup

To get started, we are using Vite. Why Vite? Because create-react-app is dead, and we don't mourn the dead here; we move on to faster tools.

For JavaScript, I run npm create vite@latest crypto-tracker-js -- --template react.

For TypeScript, it’s npm create vite@latest crypto-tracker-ts -- --template react-ts.

Both are blazingly fast. Vite doesn't care about your feelings or your language preference; it just scaffolds the project instantly. But as soon as we open the projects in VS Code, the difference slaps you in the face.

In the JavaScript project, you have your package.json, your vite.config.js, and your source files ending in .jsx. It feels lightweight. You can almost hear the wind whistling through the empty space where configuration files usually live. It invites you to just start coding.

Now, look at the TypeScript project. You see .tsx files, which is fine, but then you see tsconfig.json and tsconfig.node.json.

This file is the constitution of your project. It dictates the laws of your universe. In JavaScript, the laws are "whatever works." In TypeScript, you have to explicitly tell the compiler how strict you want to be. Do you want to allow implicit any types? Do you want to check for unused local variables? Do you want to strictly check for nulls?

For a beginner, this file is a wall of JSON that screams "Configuration Hell." You have to understand what a "target" is and how module resolution works before you even write "Hello World." For a senior engineer, however, this file is a safety blanket. It guarantees that every developer on the team is playing by the same rules.

Structure

The core difference between these two isn't just syntax; it's when you catch your mistakes. JavaScript is dynamically typed, which means variables can be anything at any time. TypeScript is statically typed, meaning once a variable is a number, it dies a number.

Let's look at the Coin component. We are fetching a list of crypto coins from an API.

const CoinRow = ({ coin }) => {
  return (
    <div className="row">
      <img src={coin.image} />
      <span>{coin.name}</span>
      <span>${coin.current_price}</span>
    </div>
  );
};

In JavaScript, I write a component that takes a prop called data.

This looks innocent. But as I'm typing coin.current_price, I am relying entirely on my own memory. I have to keep the API documentation open on a second monitor. Is it current_price or currentPrice? Is image a string URL or an object containing sizes?

If I type coin.price instead of coin.current_price, the editor doesn't care. It saves the file. I run the app. The browser renders an empty span. I spend 15 minutes console logging coin to figure out why the price is missing. This is the "Guess and Check" loop, and it burns hours of your life.

export interface Coin {
  id: string;
  symbol: string;
  name: string;
  image: string;
  current_price: number;
  high_24h: number;
  low_24h: number;
}

Now, watch the TypeScript workflow. Before I even think about the UI, I have to define the shape of my data. This is mental overhead. I have to stop, look at the API response, and translate it into an Interface.

import type { Coin } from './types';

interface Props {
  coin: Coin;
}

const CoinRow = ({ coin }: Props) => {
  return (
    <div className="row">
       {/* The moment I type "coin.", a dropdown appears */}
       <span>{coin.current_price}</span>
    </div>
  );
};

The editor knows what a coin is. If I try to access coin.price, the text turns red immediately. "Property 'price' does not exist on type 'Coin'."

This is the killer feature. I am not coding in the dark anymore. The IDE is my pair programmer, constantly whispering the correct property names in my ear. It turns the documentation into code that lives right under your cursor.

Data

export const fetchCoins = async () => {
  const res = await fetch('https://api.coingecko.com/...');
  return res.json();
};

Let's dial up the complexity. We need to fetch this data from the internet. This introduces asynchronous code and the concept of "Generics."

In JavaScript, our fetch function is simple, but dangerous.

The return value of this function is a Promise that resolves to... any. It could be an object, an array, a string, or an error message. We don't know, and JavaScript doesn't care. When we consume this function in our React component, we are flying blind.

export const fetchData = async <T>(url: string): Promise<T> => {
  const res = await fetch(url);
  if (!res.ok) {
      throw new Error('Network response was not ok');
  }
  const data = await res.json();
  return data as T;
};

In TypeScript, we want to tell the consumer of this function exactly what they are getting back. This is where we use Generics.

This generic <T> allows us to use this one fetch function for Coins, for User profiles, for anything, while maintaining strict typing.

However, there is a dirty secret here. Look at return data as T. That as keyword is a lie. We are lying to the compiler. We are saying, "I promise this JSON from the internet matches my Interface."

But what if the API changes? What if the internet goes down? TypeScript checks your code at compile time, not runtime. If the API sends back a price as a string instead of a number, TypeScript won't catch it, and your app might still crash.

To truly fix this, you would need a runtime validation library like Zod. With Zod, you define a schema that validates the data as it comes in, effectively bridging the gap between the static world of TypeScript and the chaotic world of runtime JavaScript. But that adds bundle size and complexity, which is the constant trade-off you make in this ecosystem.

Trap

Now let’s look at how we store this data in React state.

const [coins, setCoins] = useState([]);

In JavaScript, it’s simple. coins is an array. I can push numbers into it, strings, objects, or even null.

const [coins, setCoins] = useState<Coin[]>([]);

In TypeScript, inference usually works well, but sometimes we need to be explicit:

Now, if I try to setCoins(['bitcoin']), TypeScript yells at me because a string is not a Coin object. This prevents state contamination, where you accidentally store the wrong data type and break your app five steps down the line.

But here is where developers get lazy. Sometimes, TypeScript is screaming at you because your types are complex. You just want it to shut up so you can test your feature. So you do the forbidden thing.

const [data, setData] = useState<any>([]);

The any type essentially turns off TypeScript for that specific variable. It is a trap. Once you use any, it spreads like a virus. If you pass that any variable to another function, that function now accepts anything. You have successfully defeated the entire purpose of using TypeScript in the first place.

Using any is like wearing a seatbelt made of paper. It looks like safety, but it won't save you when you crash.

Refactoring

If there is one reason to switch to TypeScript, it is this: Refactoring.

Let's say our project manager decides that image is a bad name for the property. We need to rename it to imageUrl across the entire application.

In the JavaScript project, this is a nightmare scenario. I have to use "Find and Replace." I search for "image".

The search results include:

1. The actual property in the API response.
2. A CSS class named .coin-image.
3. A comment in the README.
4. A variable in a totally unrelated file.

I have to manually check every single instance. If I miss one, the image breaks. If I change the wrong one, the CSS breaks. It is anxiety-inducing.

In TypeScript, I go to my Interface.

I put my cursor on image. I press F2 to Rename. I type imageUrl and hit Enter.

VS Code analyzes the dependency graph. It knows exactly which references refer to this specific property on the Coininterface. It ignores the CSS classes. It ignores the comments. It updates the API call, the Prop types, and the Component usage in one second.

I save the file, and I have 100% confidence that I didn't break anything. This feeling of safety allows you to iterate faster. You aren't afraid to change your code because the compiler has your back.

Performance

Finally, let’s talk about performance. There is a misconception that TypeScript is slower because it has to compile.

Here is the reality: Browsers cannot run TypeScript. They only understand JavaScript. This means your TypeScript code must be erased before it ever reaches the user.

Vite handles this using esbuild. It’s incredibly fast because during development, it doesn't actually check your types. It just strips them out so the browser can run the code. This means your dev server starts almost as fast as a plain JS project.

However, for the production build, we run tsc (the TypeScript Compiler). This checks every single line of code for type errors. If there is a single error, the build fails.

This is a feature, not a bug. It prevents you from shipping broken code to production. In JavaScript, that error would have made it to the user's browser and crashed their session. In TypeScript, it crashes your build server, forcing you to fix it.

So, does TypeScript make your app faster? No. The runtime performance is identical. But does it make your development cycle faster? Over the long run, absolutely.

Verdict

So, after building this tracker twice, here is the verdict.

JavaScript is the wild, fun friend who invites you to a rave at 2 AM. It’s great for hackathons, small prototypes, and solo projects where you just want to move fast and break things. It feels fluid, unrestricted, and creative. If I have an idea I want to validate in an afternoon, I might still reach for JavaScript.

TypeScript, however, is the responsible architect. It demands a blueprint before you lay the first brick. At first, it feels restrictive. You spend time writing Interfaces instead of features. You fight with the configuration. You curse the compiler.

But as the project grows—as you add more files, more complex data structures, and more team members—TypeScript becomes the only thing keeping your sanity intact. The ability to refactor instantly, the elimination of entire classes of bugs, and the self-documenting nature of the code make it the superior choice for any serious application.

If you are looking to get hired in the industry today, TypeScript is not optional. It has won the war for attention.

So, stick with JavaScript if you want to feel like a cowboy. But learn TypeScript if you want to be an engineer.

If you want to see me suffer through building another app in the two programming languages or frameworks of your choice, then hit that subscribe button and let me know in the comments. Thanks for watching, and I will see you in the next one.