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any type

Learn how the any type turns off type checking.

The any type

The any type completely disables type checking for a variable. A variable declared as any can be assigned any type of value and you can access any property on it. This turns off TypeScript's safety.

let x: any = 5;
x = "merhaba";
x = true;
console.log(x);  // true

any is an escape hatch for data of unknown type, but it is unsafe.

any is unsafe

When any is used, TypeScript's type safety is lost. Misspelled property names do not cause compile errors and can cause runtime issues. If you do not know the type, using unknown is safer than any.

let x: any = "metin";
console.log(x.boyunUzunlugu);  // undefined, no error

any should be used sparingly; prefer specific types whenever possible.

Practice Different types with any

Declare a variable named veri of type any. First assign it "test", then reassign it 42. Print the final value with console.log.

Starter code

index.ts
// veri adında bir any değişkeni tanımla
// önce "test" değerini ata
// sonra 42 değerini yeniden ata
// son değeri yazdır

Sample solution

index.ts
let veri: any = "test";
veri = 42;
console.log(veri);

Expected output

42

Questions and answers

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

1 What does the <code>any</code> type do?

  • Prevents null assignment
  • Disables type checking for a variable Correct answer
  • Makes the variable constant
  • Allows only string values

Explanation: <code>any</code> turns off all type checks on a variable; any type of value can be assigned and any property can be accessed.

2 Add the any type

Question 
let deger: ____ = "merhaba";
deger = 100;
Answer 
let deger: any = "merhaba";
deger = 100;

Explanation: Since the variable takes both a string and a number, only <code>any</code> allows both assignments; <code>string</code> or <code>number</code> would fail on the other assignment.

3 any concepts

Term Meaning
any Disables type checking
let x: any = 5; x = "a"; Allows changing type
any ile erişim Any property can be accessed
any kaçış yolu Unsafe but flexible

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