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Display

Write the function that formats the weather.

What is a display function?

A display function converts weather data into a string to show the user. It combines city, temperature, and condition information with the + operator. This keeps model data separate from the user interface text.

function format(h: Weather): string {
  return h.city + " " + h.temperature + "C";
}

String concatenation

During formatting, text pieces are combined with the + operator. Numeric values are automatically converted to strings. For example, "Bursa" + " " + 20 + "C" gives "Bursa 20C". This method produces a simple and readable output.

Practice formatla function

Define a Hava interface: sehir: string, sicaklik: number. The formatla function should be (h: Hava): string and return h.sehir + " " + h.sicaklik + "C". Print the result of calling formatla({ sehir: "Bursa", sicaklik: 20 }) with console.log.

Starter code

index.ts
// Hava interface tanımla: sehir, sicaklik
// formatla fonksiyonu string dönsün
// sehir + " " + sicaklik + "C" birleştir
// formatla çağırıp yazdır

Sample solution

index.ts
interface Hava { sehir: string; sicaklik: number; }
function formatla(h: Hava): string {
  return h.sehir + " " + h.sicaklik + "C";
}
console.log(formatla({ sehir: "Bursa", sicaklik: 20 }));

Expected output

Bursa 20C

Questions and answers

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

1 What type does the formatla function return?

  • string Correct answer
  • boolean
  • void
  • number

Explanation: Since the display function produces the text to show the user, it returns a string value.

2 String concatenation operator

Question 
function formatla(h: Hava): string {
  return h.sehir + " " + h.sicaklik ____ "C";
}
Answer 
function formatla(h: Hava): string {
  return h.sehir + " " + h.sicaklik + "C";
}

Explanation: The + operator is used to concatenate strings; numeric values are automatically converted to strings.

3 Display concepts

Term Meaning
formatla Formatting function
string Return type
+ String concatenation
Hava Input type

All lessons in Intermediate

1 Classes

  1. Class basics
  2. Constructor and fields
  3. Methods
  4. Static members
  5. Summary - Classes

2 Access modifiers

  1. public
  2. private
  3. protected
  4. Parameter properties
  5. Summary - Access modifiers

3 Readonly properties

  1. readonly fields
  2. Readonly parameter
  3. Readonly vs const
  4. Summary - Readonly

4 Generics

  1. What is a generic?
  2. Generic functions
  3. Generic classes
  4. Multiple type parameters
  5. Summary - Generics

5 Generic constraints

  1. extends constraint
  2. keyof constraint
  3. Default type parameter
  4. Summary - Generic constraints

6 Utility types

  1. Partial
  2. Required and Pick
  3. Omit and Record
  4. Summary - Utility types

7 keyof and typeof

  1. keyof operator
  2. typeof operator
  3. Indexing with keyof
  4. Summary - keyof and typeof

8 Mapped types

  1. What is a mapped type?
  2. Readonly mapped type
  3. Optional mapped type
  4. Summary - Mapped types

9 Conditional types

  1. What is a conditional type?
  2. Distributive conditional
  3. Logic with conditional
  4. Summary - Conditional types

10 infer

  1. infer keyword
  2. Extracting from Promise
  3. Array element type
  4. Summary - infer

11 Decorators

  1. What is a decorator?
  2. Method decorator
  3. Property decorator
  4. Decorator factories
  5. Summary - Decorators

12 Modules

  1. export and import
  2. Default export
  3. Re-export
  4. Type-only import
  5. Summary - Modules

13 Namespaces

  1. What is a namespace?
  2. Nested namespace
  3. Namespace vs module
  4. Summary - Namespaces

14 Declaration files

  1. What is .d.ts?
  2. Ambient module
  3. Triple-slash directive
  4. Summary - Declaration files

15 Advanced classes

  1. abstract class
  2. implements
  3. Get and set
  4. Summary - Advanced classes

16 Type assertion

  1. as keyword
  2. angle bracket syntax
  3. Type assertion vs casting
  4. Casting from unknown
  5. Summary - Type assertion

17 Project: Library package

  1. Package design
  2. Exporting types
  3. Generic helpers
  4. Declaration file
  5. Integration

18 Project: Quiz app

  1. Question model
  2. Question pool
  3. Answer check
  4. Score calculation
  5. Integration

19 Project: Weather app

  1. Weather model
  2. API response type
  3. Data transform
  4. Display
  5. Integration

20 Intermediate final

  1. Challenge 1: Classes
  2. Challenge 2: Generics
  3. Challenge 3: Type systems
  4. Challenge 4: Mini app