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Summary - TypeScript basics

Write your first TypeScript program by combining setup, tsc, and tsconfig.

Summary - TypeScript basics

TypeScript is a typed superset of JavaScript. The tsc compiler turns .ts files into .js while checking types. With tsconfig.json you set the compile options and the target JS version.

// app.ts
let mesaj: string = "Merhaba TypeScript";
console.log(mesaj);
// Compile: tsc app.ts
// Run: node app.js

This way you write a safe program that catches errors early.

Practice Your first TypeScript program

Declare a variable ad with type string and value "TS". Declare a variable selam with type string and value "Öğreniyorum ". Then print the concatenation selam + ad with console.log.

Starter code

index.ts
// ad değişkeni: string, değer "TS"
// selam değişkeni: string, değer "Öğreniyorum "

// selam + ad birleşimini yazdır

Sample solution

index.ts
let ad: string = "TS";
let selam: string = "Öğreniyorum ";
console.log(selam + ad);

Expected output

Öğreniyorum TS

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which file specifies the compiler options in a TypeScript project?

  • package.json
  • README.md
  • tsconfig.json Correct answer
  • .gitignore

Explanation: tsconfig.json tells tsc the target JS version, the output folder, and which files to compile. package.json lists package dependencies.

2 Type annotation

Question 
let mesaj: ____ = "Merhaba TypeScript";
Answer 
let mesaj: string = "Merhaba TypeScript";

Explanation: "Merhaba TypeScript" is a string; so the type must be string. Assigning number or boolean gives a compile error.

3 TypeScript core parts

Term Meaning
tsc Compiler
tsconfig.json Configuration
.ts Source extension
target JS version

All lessons in Beginner

1 TypeScript intro and setup

  1. What is TypeScript?
  2. Why TypeScript?
  3. tsc compiler
  4. tsconfig basics
  5. Summary - TypeScript basics

2 Primitive types

  1. string type
  2. number type
  3. boolean type
  4. let and const
  5. Summary - Primitive types

3 Arrays

  1. Array type
  2. Array methods
  3. readonly arrays
  4. Multidimensional arrays
  5. Summary - Arrays

4 Tuples

  1. What is a tuple?
  2. Tuple usage
  3. readonly tuple
  4. Summary - Tuple

5 Enums

  1. Numeric enum
  2. String enum
  3. const enum
  4. Enum members
  5. Summary - Enum

6 any, unknown, never

  1. any type
  2. unknown type
  3. never type
  4. void type
  5. Summary - Special types

7 Type annotation

  1. Variable annotation
  2. Parameter annotation
  3. Return type annotation
  4. Summary - Type annotation

8 Type inference

  1. Basic inference
  2. Inference with const
  3. Best common type
  4. Summary - Type inference

9 Objects

  1. Object type
  2. Optional properties
  3. Readonly properties
  4. Summary - Objects

10 Functions

  1. Function declaration
  2. Optional and default params
  3. Rest params
  4. Function overloads
  5. Summary - Functions

11 Arrow functions

  1. Arrow syntax
  2. this with arrow
  3. Arrow type
  4. Summary - Arrow functions

12 Interfaces

  1. What is an interface?
  2. Property types
  3. Interface vs type alias
  4. Summary - Interfaces

13 Type alias

  1. What is a type alias?
  2. Composition with alias
  3. Alias vs interface
  4. Summary - Type alias

14 Union and intersection

  1. Union types
  2. Intersection types
  3. Literal types
  4. Summary - Union & intersection

15 null and undefined

  1. null vs undefined
  2. Optional chaining
  3. Nullish coalescing
  4. Summary - null & undefined

16 Strict mode

  1. strict: true
  2. strictNullChecks
  3. strictFunctionTypes
  4. Summary - Strict mode

17 Project: Shopping cart

  1. Cart design
  2. Add product
  3. Total calculation
  4. Apply discount
  5. Integration

18 Project: Todo CLI

  1. Task model
  2. Add and list
  3. Completion
  4. Filtering
  5. Integration

19 Project: Library

  1. Book model
  2. Add and search
  3. Borrow
  4. Return
  5. Integration

20 Beginner final

  1. Challenge 1: Types
  2. Challenge 2: Functions
  3. Challenge 3: Unions
  4. Challenge 4: Mini app