Why TypeScript?

Learn how type safety catches errors early.

Why TypeScript?

TypeScript catches type errors at compile time, not at runtime. So if a function expects a number and you pass a string, the compiler warns you.

function topla(a: number, b: number): number {
  return a + b;
}
topla(5, "10"); // Compile error

This way you spot errors during writing, not in production.

Type safety

Type safety ensures that variables and parameters are used only with their expected types. TypeScript flags wrong usage, preventing unexpected crashes.

let bitti: boolean = false;
bitti = "evet"; // Error: string is not assignable to boolean

This makes the code's behavior more predictable.

Exercise Type-safe function

Write a function named kareAl. Its parameter is x: number, its return type is number. Its body returns x * x. Then print the result of kareAl(6) with console.log.

Show example solution

function kareAl(x: number): number {
  return x * x;
}
console.log(kareAl(6));

Test yourself

When does TypeScript catch type errors?
- Only in the browser
- At compile time
- Only in production
- At runtime
Show answer

At compile time — The TypeScript compiler checks types during compilation. This lets you see errors before running the code.

Pick the right type

let acik: ____ = true;

Show answer

let acik: boolean = true;

Error catching times

Derleme zamanı

Errors caught while writing
Tür açıklaması

Specifies the expected type
Çalışma zamanı

When JS catches errors
Tür güvenliği

Prevents wrong usage

Next lesson: tsc compiler

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