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
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
// 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!