Course/Module 1/Topic 1 of 4Beginner

What is TypeScript?

TypeScript is JavaScript with types. It catches errors before your code runs, making large codebases safer and easier to maintain. This is a foundational concept in type-safe JavaScript development that professional developers rely on daily. The explanations below are written to be beginner-friendly while covering the depth and nuance that comes from real-world TypeScript experience. Take your time with each section and practice the examples

15 min•By Priygop Team•Last updated: Feb 2026

What is TypeScript?

TypeScript is a superset of JavaScript created by Microsoft in 2012. It adds optional static typing to JavaScript. TypeScript code compiles to plain JavaScript and runs anywhere JavaScript runs. The key benefit: TypeScript catches type errors at compile time (before running), while JavaScript only shows errors at runtime. This makes TypeScript especially valuable for large projects and teams.

Why Use TypeScript?

Catch errors early — type errors are caught at compile time, not runtime
Better IDE support — autocomplete, refactoring, and navigation
Self-documenting code — types serve as documentation
Safer refactoring — the compiler tells you what broke
Used by Angular, Next.js, NestJS, and most large projects
Prerequisite: You should know JavaScript basics first

TypeScript vs JavaScript

Example

// JavaScript — no types, errors only at runtime
function add(a, b) {
    return a + b;
}
console.log(add(5, "10")); // "510" — wrong! No error shown

// TypeScript — types catch the error immediately
function add(a: number, b: number): number {
    return a + b;
}
// add(5, "10"); // ERROR: Argument of type 'string' is not assignable to 'number'
console.log(add(5, 10)); // 15 — correct!

Try It Yourself: TypeScript Concepts

Try It Yourself: TypeScript ConceptsJavaScript

JavaScript Editor

✓ ValidTab = 2 spaces

// TypeScript compiles to JavaScript — let's see the concepts in action
// (We simulate TypeScript behavior in JavaScript here)

// In TypeScript you write:
// let name: string = "Alice";
// let age: number = 25;
// let isStudent: boolean = true;

// This compiles to JavaScript:
let name = "Alice";
let age = 25;
let isStudent = true;

console.log("Name:", name);
console.log("Age:", age);
console.log("Is Student:", isStudent);

// TypeScript would catch this error:
// age = "twenty-five"; // ERROR in TypeScript!
// But JavaScript allows it (no type safety)
age = 26; // OK — still a number
console.log("Updated age:", age);

// TypeScript function with types:
// function greet(person: string): string { return "Hello, " + person; }
function greet(person) {
    return "Hello, " + person + "!";
}
console.log(greet("World"));

Result

Click ▶ Run to see the result

Edit the code on the left, then click Run

JavaScript|29 lines|830 chars|✓ Valid syntax

UTF-8

Quick Quiz

Topics in This Module

Course/Module 1/Topic 1 of 4Beginner

What is TypeScript?

15 min•By Priygop Team•Last updated: Feb 2026

What is TypeScript?

Why Use TypeScript?

Catch errors early — type errors are caught at compile time, not runtime
Better IDE support — autocomplete, refactoring, and navigation
Self-documenting code — types serve as documentation
Safer refactoring — the compiler tells you what broke
Used by Angular, Next.js, NestJS, and most large projects
Prerequisite: You should know JavaScript basics first

TypeScript vs JavaScript

Example

// JavaScript — no types, errors only at runtime
function add(a, b) {
    return a + b;
}
console.log(add(5, "10")); // "510" — wrong! No error shown

// TypeScript — types catch the error immediately
function add(a: number, b: number): number {
    return a + b;
}
// add(5, "10"); // ERROR: Argument of type 'string' is not assignable to 'number'
console.log(add(5, 10)); // 15 — correct!

Try It Yourself: TypeScript Concepts

Try It Yourself: TypeScript ConceptsJavaScript

JavaScript Editor

✓ ValidTab = 2 spaces

// TypeScript compiles to JavaScript — let's see the concepts in action
// (We simulate TypeScript behavior in JavaScript here)

// In TypeScript you write:
// let name: string = "Alice";
// let age: number = 25;
// let isStudent: boolean = true;

// This compiles to JavaScript:
let name = "Alice";
let age = 25;
let isStudent = true;

console.log("Name:", name);
console.log("Age:", age);
console.log("Is Student:", isStudent);

// TypeScript would catch this error:
// age = "twenty-five"; // ERROR in TypeScript!
// But JavaScript allows it (no type safety)
age = 26; // OK — still a number
console.log("Updated age:", age);

// TypeScript function with types:
// function greet(person: string): string { return "Hello, " + person; }
function greet(person) {
    return "Hello, " + person + "!";
}
console.log(greet("World"));

Result

Click ▶ Run to see the result

Edit the code on the left, then click Run

JavaScript|29 lines|830 chars|✓ Valid syntax

UTF-8

Quick Quiz

Topics in This Module

Module 1: Introduction to TypeScript - Free TypeScript Course | Priygop | Priygop