Typescript Mini Reference: A Quick Guide to the Typescript Programming Language for Busy Coders

Preface....11

Dear Readers:....14

1. Introduction....16

2. Typescript Basics....22

2.1. What is Typescript?....22

2.2. Static Typing....26

2.2.1. Type annotations....26

2.2.2. Static type checking....26

2.2.3. Type inference....28

2.3. Notes on Development Process....29

2.4. The Typescript Compiler....31

2.5. Typescript JSON Configuration File....34

2.5.1. Top-level options....34

2.5.2. compilerOptions....36

2.5.3. strict....39

2.5.4. strictNullChecks....39

2.5.5. noImplicitAny....40

2.5.6. noImplicitThis....40

3. Module System....42

3.1. ES Modules....42

3.2. Typescript Modules....43

3.3. Module Exports....43

3.3.1. (Regular) exports....44

3.3.2. Default exports....46

3.4. Module Imports....47

3.4.1. Module import....47

3.4.2. import - from Declaration....48

3.4.3. Default import....48

3.4.4. Name list import....48

3.4.5. Namespace import....49

3.5. Typescript Namespaces....49

4. Variables....50

4.1. The const Declaration....50

4.2. The let Declaration....51

4.3. The var Declaration....53

5. Basic Types....55

5.1. Javascript Types....55

5.1.1. The typeof operator....56

5.1.2. The instanceof operator....57

5.2. Strict Equality....58

5.3. Primitive Types....59

5.3.1. The boolean, number, and string types....59

5.3.2. The bigint Type....60

5.3.3. The symbol type....60

5.4. Literal Types....61

5.5. The any Type....62

5.6. The unknown Type....63

5.7. The null and undefined Types....65

5.8. The never Type....67

5.9. The void Type....68

5.10. The object Type....69

5.11. Function Types....70

5.12. Array Types....71

5.13. Tuple Types....72

5.14. Enum Types....74

6. Type Aliases....76

7. Type Annotations....79

7.1. Variable Annotations....79

7.2. Function Annotations....80

8. Assertions....84

8.1. Type Assertions....84

8.2. Const Assertions....85

8.3. Non-Null Assertions....87

9. Generics....89

9.1. Why Generics?....89

9.2. Generic Functions....93

9.3. Generic Types....95

9.4. Generic Type Constraints....96

10. Arrays....98

10.1. Generic Array....98

10.1.1. Array creation....99

10.1.2. Array iteration....100

10.2. Generic ReadonlyArray....101

11. Algebraic Data Types....103

11.1. Tuples....103

11.1.1. Fixed-size tuples....103

11.1.2. Generic tuples....105

11.1.3. Variadic tuples....105

11.2. Readonly Tuples....108

11.3. Union Types....109

11.3.1. Narrowing....111

11.4. Discriminated Unions....112

11.5. Intersection Types....114

12. Function Types....116

12.1. Function Definitions....116

12.2. Arrow Function Definitions....117

12.3. Function Types....118

12.3.1. Function type expressions....118

12.3.2. Function return types....120

12.3.3. Generic function alias....121

12.3.4. The Function type....121

12.4. Parameter List....122

12.4.1. Parameter initializers....123

12.5. Optional Parameters....123

12.6. The Rest Parameter....125

12.7. Parameter Destructuring....128

12.8. The this Parameter....130

12.8.1. Global context....131

12.8.2. Function context....131

12.9. Typescript Function Overloading....133

12.9.1. Overload signatures vs the implementation signature....133

13. Object Types....136

13.1. Object Literal Types....136

13.1.1. The empty object literal type....138

13.2. Object Type Members....139

13.2.1. Optional properties....139

13.2.2. Readonly properties....140

13.3. Index Signatures....142

13.3.1. Typescript index signatures....143

13.4. Getters and Setters....145

13.5. Member Methods....148

13.5.1. Method overloading....149

13.6. Structural Subtyping....149

14. Interfaces....152

14.1. Interface Types....152

14.2. Extending Interfaces....154

15. Classes....156

15.1. The ECMAScript Class....156

15.1.1. Class declaration....156

15.1.2. Class body....157

15.1.3. Fields....158

15.1.4. Accessors....159

15.1.5. Methods....159

15.1.6. Constructors....159

15.1.7. Static blocks....160

15.1.8. Inheritance....160

15.2. The Typescript Class....160

15.2.1. Constructors....161

15.2.2. Member visibility....162

15.2.3. Parameter properties....163

15.3. Abstract Classes....164

15.4. Implementing Interfaces....166

15.4.1. Implementing multiple interfaces....168

15.5. Generic Classes....169

16. Type Narrowing....171

16.1. Control Flow Analysis....171

16.2. The typeof Type Guard....171

16.3. The instanceof Type Guard....172

16.4. The in Operator Narrowing....174

16.5. Discriminated Unions....175

17. Advanced Types....179

17.1. Template Literal Types....179

17.2. The typeof Type Operator....180

17.3. The keyof Type Operator....181

17.4. Indexed Access Types....182

17.5. Conditional Types....183

17.6. Mapped Types....184

Appendix A: How to Use This Book....186

About the Author....190

About the Series....192

Community Support....194

Become a Better Javascript Programmer!

Typescript is a better Javascript, It is a statically typed, safe programming language, which uses more or less the same syntax as Javascript. Typescript programs are compiled to Javascript, and they can be run anywhere Javascript is supported. It is widely used by professional Javascript developers, for frontend development (e.g., Angular, React, and VueJS) as well as for backend development (e.g., Node.Js and Deno).

This book is a "mini" language reference on the Typescript programming language. We go through all essential features of Typescript (as of versions 4.8 and 4.9), and some new ECMAScript features, in this book.

Although it is written as a reference, however, you can read it more or less from beginning to end and you should be able to get the overall picture of the Typescript language if you have some prior experience with programming in Typescript or modern Javascript (ES2015 and later).

The book covers

• Typescript development basics.
• ES module system.
• Basic JS/TS types. Type annotations.
• Variable declarations. Type inference.
• Algebraic data types. Generics.
• Objects. Classes.
• Function types. Arrow functions.
• How to create new types from existing types.