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Summary - Primitive types

Write a profile card by combining string, number, and boolean types.

The three primitive types

So far you have seen three primitive types: string for text, number for numbers (integer or decimal), and boolean for two-state logic. You also learned to declare variables with let and const.

let isim: string = "Ece";
let yas: number = 28;
let aktif: boolean = true;
const dil = "TypeScript";

These four pieces are the foundation of TypeScript.

Practice Use the three types together

Declare three variables: urun (string, value "Kalem"), adet (number, value 3), stokta (boolean, value true). Print all three with a single console.log.

Starter code

index.ts
// urun (string), adet (number), stokta (boolean) tanımla

// üçünü tek console.log ile yazdır

Sample solution

index.ts
let urun: string = "Kalem";
let adet: number = 3;
let stokta: boolean = true;
console.log(urun, adet, stokta);

Expected output

Kalem 3 true

Questions and answers

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

1 Which of the following lines uses the correct types?

  • let x: number = "5"; let y: string = a; let z: boolean = true;
  • let x: int = 5; let y: string = "a"; let z: float = 3.14;
  • let x: number = 5; let y: text = "a"; let z: bool = true;
  • let x: number = 5; let y: string = "a"; let z: boolean = true; Correct answer

Explanation: number, string, and boolean are written lowercase; the values must also match the type.

2 Fill in the missing value

Question 
let tam: number = 42;
let metin: string = ____;
let dogru: boolean = true;
Answer 
let tam: number = 42;
let metin: string = "kod";
let dogru: boolean = true;

Explanation: A string variable must be assigned a text value (in quotes); a word without quotes is treated as a variable, and 42 and true are different types.

3 Primitive types and keywords

Term Meaning
string text type
number numeric type
boolean logical type
const constant variable

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