JavaScript vs TypeScript: Complete Guide for Developers

This content originally appeared on DEV Community and was authored by Prachi Gupta

JavaScript has been the go-to language for web development for years. But as web apps became bigger and more complex, developers started needing something more structured. That’s where TypeScript comes in.

In this blog, we’ll explore everything about JavaScript vs TypeScript — their differences, features, pros and cons, and answer a common question: “If TS has features that JS doesn’t, how does it still work after compiling?”

Let’s dive in

What is JavaScript?

JavaScript is a dynamic, interpreted, and loosely typed programming language. It runs in browsers and on servers (via Node.js). It’s the core language of the web.

Key Features:

• Dynamically typed (no need to declare types)
• Interpreted at runtime
• Runs in any browser
• Used in frontend, backend, mobile, desktop apps

Example:

let message = "Hello!";
console.log(message);

You don’t define the type of message — it’s handled automatically.

What is TypeScript?

TypeScript is a superset of JavaScript developed by Microsoft. It adds optional static typing, advanced features, and tooling support — and compiles down to regular JavaScript.

Key Features:

• Statically typed (you can define variable types)
• Type checking at compile time
• Needs to be compiled to JavaScript using tsc
• Great tooling: autocompletion, refactoring, and IntelliSense
• Can use all JavaScript features + more

Example:

let message: string = "Hello!";
console.log(message);

Here, message must always be a string.

JavaScript vs TypeScript: Full Comparison

Features Available in TypeScript but Not in JavaScript

These features do not exist in JavaScript, but help developers during development:

1. Type Annotations

let age: number = 25;

Ensures age can only be a number.

2. Interfaces

interface User {
  id: number;
  name: string;
}

Helps define the structure of objects.

3. Enums

enum Role {
  Admin,
  User,
}

Compiles into JavaScript object mappings.

4. Generics

function identity<T>(value: T): T {
  return value;
}

Makes functions reusable for multiple types.

5. Access Modifiers (in classes)

class Person {
  private name: string;
}

Helps with object-oriented programming.

6. Tuples

let pair: [string, number] = ["age", 25];

Allows mixed-type arrays with fixed positions.

Pros and Cons of JavaScript

Pros:

• Easy to learn
• No setup needed
• Supported everywhere (browser/server)
• Massive community and resources
• Fast for prototyping

Cons:

• No type safety
• Hard to debug in large apps
• Runtime errors
• Loose syntax = more room for bugs
• Inconsistent behavior across environments

Pros and Cons of TypeScript

Pros:

• Type-safe: fewer runtime errors
• Great for teams and large projects
• Advanced editor support (VS Code)
• Easier to refactor and maintain
• Improves code readability

Cons:

• Needs compilation step
• Slightly harder to learn
• More boilerplate code
• Slower to prototype
• Not natively understood by browsers

How Does TypeScript Work If JS Doesn’t Understand TS-only Features?

This is the most common question — and it’s a smart one!

Short Answer:

TypeScript exists only during development. After compiling with tsc, all TS-only features (like types, interfaces) are stripped out, and the output is clean JavaScript.

Compile-Time Only Features:

Feature	Exists After Compilation?
string, number, boolean types	Removed
interface, type	Removed
generics	Removed
enums	Converted to JS object
Access modifiers	Removed (structure only)

Example:

TypeScript Code:

function greet(name: string): string {
  return "Hello, " + name;
}

Compiled JavaScript:

function greet(name) {
  return "Hello, " + name;
}

No :string anywhere — types are gone. But they helped catch errors during development.

Think of TypeScript as a code-checking assistant — it helps you write better code, but steps out of the way when it’s time to run the app.

Final Thoughts

TypeScript doesn’t replace JavaScript — it enhances it. Start with JavaScript to understand the fundamentals, then switch to TypeScript when your projects grow.

What do you prefer?

Are you #TeamJS or #TeamTS? Let me know in the comments!

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This content originally appeared on DEV Community and was authored by Prachi Gupta