TypeScript vs. JavaScript: Key Differences


TypeScript and JavaScript are both widely used programming languages for web development. While they share similarities, they also have key differences that make each suitable for specific use cases. In this guide, we'll explore the fundamental differences between TypeScript and JavaScript, providing sample code to illustrate these distinctions.

TypeScript and JavaScript: An Overview

TypeScript: TypeScript is a statically typed superset of JavaScript developed by Microsoft. It adds static typing to JavaScript and compiles to plain JavaScript code. TypeScript is known for its strong type checking and tooling support.

JavaScript: JavaScript is a dynamic, weakly typed scripting language that's commonly used for web development. It's interpreted by web browsers and can be run on both the client and server side.

Key Differences

1. Static Typing

TypeScript uses static typing, which means that variable types are declared at compile-time. JavaScript, on the other hand, uses dynamic typing, allowing variables to change types at runtime.

Sample TypeScript Code:

// TypeScript code
let message: string = "Hello, TypeScript";
message = 42; // Error: Type 'number' is not assignable to type 'string'.

Sample JavaScript Code:

// JavaScript code
let message = "Hello, JavaScript";
message = 42; // No type error in JavaScript

2. Compile-Time Checking

TypeScript performs static analysis during compilation to catch type-related errors. JavaScript relies on runtime checks, which may lead to errors being discovered only during execution.

Sample TypeScript Code:

// TypeScript code
function add(a: number, b: number): number {
return a + b;
add(10, '5'); // Error: Argument of type 'string' is not assignable to parameter of type 'number'.

Sample JavaScript Code:

// JavaScript code
function add(a, b) {
return a + b;
add(10, '5'); // No error in JavaScript; it will concatenate the strings

3. Optional Features

TypeScript supports optional features like interfaces, decorators, and namespaces, which are not part of the ECMAScript standard. JavaScript adheres to the ECMAScript standard, which doesn't include these features.

Sample TypeScript Code (Using Interfaces):

// TypeScript code with an interface
interface Person {
name: string;
age: number;
const person: Person = { name: "Alice" };

Sample JavaScript Code (No Interfaces):

// JavaScript code
const person = { name: "Alice" };

4. Tooling and IDE Support

TypeScript provides robust tooling and IDE support, including code completion, type checking, and refactoring capabilities. While JavaScript also enjoys good tooling, TypeScript's tooling is more advanced due to its static typing.


Both TypeScript and JavaScript have their strengths and use cases. The decision to use one over the other depends on project requirements, team expertise, and the level of type safety and tooling support needed. Understanding the key differences between TypeScript and JavaScript is essential for making informed choices in your web development projects.