Typescript Fundamentals Beginners Tutorial

TypeScript is an open-source object-oriented language developed and maintained by Microsoft. It is a typed superset of JavaScript that compiles to plain JavaScript. Will learn/review the new keywords-let, const and function/object syntax also shows how the new class, interface, module syntax can be used with JavaScript library like Angular, React, Node. TypeScript is pure object oriented with classes, interfaces, modules, import, export and statically typed like C# or Java. The popular JavaScript framework Angular 2.x and above versions are written in TypeScript. Mastering TypeScript can help developers and programmers to write object-oriented programs and have them compiled to JavaScript, both on the server side and client side.

Prerequisites for current course / What you need to know

TypeScript introduces us to the newest language features that can be used in JavaScript code. Due to this, I assume you have some working knowledge/understanding of JavaScript. If you haven't, will recommend watching JavaScript Essentials Tutorial for beginners. Basic knowledge of JavaScript is required, having a good understanding of OOP concepts and advanced JavaScript is an added advantage. Finally, you will be using a bit of Angular.js, React.js, and Node.js but nothing that requires deep/advanced knowledge.

Topics include

Section 1. Course Introduction

1.1. Welcome

Hi All, I'm Dinanath Jayaswal, Senior UI/Web Developer and Adobe Certified Expert Professional, I wanna welcome you to Typescript fundamentals beginners tutorial. In this course/tutorial will go over how to start with using the Typescript features right with the bang. Will dive into the specifics of Typescript and new features it includes. We'll look at new keywords, syntax, and operators that can be used to simplify code structure. At the end we'll take a look at class, module syntax in Typescript and how that can be used immediately with very popular JavaScript library/frameworks like Angular, React, Node, etc. Let us explore and learn some pretty exciting stuff so let's go ahead and get started with Typescript.

Typescript will introduce us to the newest language features that can be used in JavaScript code - The Modern JavaScript.

1.2. Who is this for?

This course is for anyone and everyone, Almost everyone! who is interested in boost skills and further career - by learning new latest programming/coding standards/features/syntaxes/keywords introduced in the latest version of JavaScript to become a hi-tech developer. Programmers/Developers coming from any language wants to make a career in Web Technologies can learn Typescript.

Section 2. Introduction to Typescript

2.1. What is Typescript?

Typescript is Open source/free, exciting, dynamic new development language, library from Microsoft
TypeScript is a strongly typed, object oriented, compiled language
It was designed and developed by Anders Hejlsberg (designer of C#) at Microsoft
Typed superset of JavaScript which Compiles to plain JavaScript
It consists of variables Data Types string, number, boolean, etc. but it is optional
One can write safer/meaningful/easily maintainable/scalable code
The developer can Identify mistakes during development/compilation step (scope of the variable, function parameter, variable datatype mismatch, etc.)
Angular latest version uses typescript as an official/primary development language
Typescript = ECMAScript 5 + 6 + 7 + Latest features
TypeScript is JavaScript plus some additional features, Typescript is a language that is meant to be compiled into JavaScript:
- Typescript => JavaScript OR .ts => .js

2.2. Why Typescript?

Typescript got a similar syntax to JavaScript
Typescript integrates easily into JavaScript projects
TypeScript is extended JavaScript and superior to its other counterparts like CoffeeScript and Dart programming languages in a way that extends JavaScript
Currently, it is used in many large projects and many libraries written/developed fully in Typescript:
- Google Angular 2.x and greater version,
- WinJS (The Windows library for JavaScript)
The TypeScript transpiler provides the error-checking feature
TypeScript comes with an optional static typing and types inference system through the TLS (TypeScript Language Service)
Prevent bugs (data type)
TypeScript supports Object Oriented Programming concepts like classes, interfaces, inheritance, etc.
Increases the code quality, readability and makes it an easy to maintain and refactor the code base
Also integrated with task runners like Grunt & Gulp
Rapid growth and use

2.3. Components of TypeScript

Language − syntax, keywords, and type annotations
TSC TypeScript Compiler − converts TypeScript to JavaScript equivalent
TLS TypeScript Language Service − Supports editor operations like static typing and type inference system, statement completion, code formatting, etc.

Section 3. Setting up Typescript Development Environment

3.1. Installing Node, NPM and Typescript

Install node from https://nodejs.org/en/
Open up your terminal window/command prompt (cmd, git bash, node command prompt) to run some of node commands
Verify and check node installation/version by using command: node -v
install typescript globally by using command: npm install -g typescript
Verify typescript Installation by command: tsc (tsc = typescript compiler)
Verify typescript Installation and version both with command: tsc -v or tsc --version
Install and use some text editor or IDE (Integrated Development Environment) like Notepad++, Sublime Text, Adobe Brackets, Visual Studio Code to type code

3.2. Write first Typescript code/program

Create a new folder to store all typescript/.ts example files
Create a first .ts file and type basic javascript/typescript or valid javascript code
Now by using node/npm command compile .ts file into .js, command: tsc file.ts
Use type annotation to eliminate any data variable type error: let name:string = 'Dinanath';
We can use/run .js files in browser or in NodeJs (node command to run any .js file: node file.js), NodeJs can not run/understand .ts file
Use automatic compilation method using watch mode: tsc file.ts --watch

// by default typescript consider all files in a folder as a module, so variables defined in one file will be checked on the fly and throws an error: Cannot redeclare block-scoped variable - to solve issue use export {}

export {};

// write valid javascript, basic javascript/typescript
console.log('Welcome to typescript');
// ------------------------------

//type annotation to eliminate any data variable type error
let name:string = 'Dinanath';
//name=123; // error
console.log('My Name is: ' + name);

3.3. TypeScript Playground

Write and test Typescript without download or install anything: https://www.typescriptlang.org/play

3.4. ScratchJS

Alternatively, Simply we can add/install a Google Chrome Extention named Scratch JS, an add-on for DevTools which integrates both the Traceur and Babel transpilers, allowing us to test out the new JS features coming with ES6/ES2015
Scratch JS also supports CoffeeScript, LiveScript and more compile-to-JS languages will be added soon
To install Scratch JS as a Google Chrome Extention:
- In google chrome web store https://chrome.google.com/webstore/category/extensions?hl=en-GB or at https://www.google.com/ search for Scratch JS
- From searched result select Scratch JS and click -> ADD to Chrome
Once extension installed properly, open developer tool (F12, Fn12, Right Click on web page Inspect), click on ScratchJS - at left side type ES6 code and right side check ES5 output

Section 4. Typescript latest features-concepts

4.1. TypeScript - Basic Syntax

Syntax is nothing but a set of rules for writing programs. A TypeScript program simply composed of:

Statements and Expressions
Variables
Functions
Comments
Modules

4.2. Variable Declarations

4.2.1. Variable

A variable is container to store/hold the data/information
A variable is a kind of data holder where we can store some value for programming or calculation purpose
A JavaScript variable is simply a name of the storage location (named containers/named storage) for data
Variables are symbolic names for values
Variables are used to store data of different types like a string of text, numbers, boolean values like true/false, an array of data, etc.
The data or value stored in the variables can be set, updated, and retrieved whenever needed
TypeScript follows the same variable declarations rules as JavaScript, Variables can be declared using: var, let, and const

4.2.2. `var` Variable Declarations

Variables are declared traditionally using the keyword: var keyword
Many things what we do in plain JavaScript works exactly same with typescript (like declaring a variable with var)
Vanilla JavaScript var and scope are tricky, they hoist also it has global and functional scope but not block level scope
var keyword variables can be re-declared n number of times
The assignment operator (=) is used to assign value to a variable, like this: var varName = value; or var firstName = 'JavaScript';
Example: Variables are like box or an envelope which we use to organize various kinds of stuff and put a label on each box or an envelope
Example: Variable declaration and assignment is just like Maths & Algebra: x = 10; and in JavaScript we write var x = 10;

export {};

var name: string = 'Dinanath';
var age: number = 35;
var isDeveloper: boolean = true;
console.log('My details are : ' + name + ' ' + age + ' ' + isDeveloper);

var name = 'Dino';
console.log('My name is : ' + name);

4.2.3. `let` Variable Declarations

Typescript encourages programmers to use let and const keyword-based variables
let and const variables have block level scope also they can not be re-declared multiple times
To deal with scope in JavaScript we have new keyword named let used to declare variables
We use the let keyword to create block scoping in JavaScript in locations where we weren't able to do so before
Let keyword block scope - let keyword variables exist only inside block { }scope
let keyword variables cannot be used before the declaration (never hoisted)
let keyword variables can not be re-declared

export {};

let name: string = 'Dinanath';
let age: number = 35;
let isDeveloper: boolean = true;
console.log('My details are : ' + name + ' ' + age + ' ' + isDeveloper);

// let variables not be re-declared
// let name: string = 'Dino';

4.2.4. `const` Variable Declarations (also known as `"immutable variables"`)

Typescript encourages programmers to use let and const keyword-based variables
let and const variables have block level scope also they can not be re-declared multiple times
Like the let keyword, we can also use const an alternative for declaring variables
const is short for constant allows us to set constant variables which shouldn't be reassigned
We can not change the value of const variable, so use const to define fixed set of values also to protect the values of certain variables
Creating/Using an existing const variable again or re-assigning value to const variable generates TypeError, SyntaxError
the const keyword is used to define/create variable with read-only constants
const must have some value while declaration/initialized
const value is fixed, not to change/re-assigned in future
const is also having block scope
the const value never hoisted
However, we can still change object properties or array elements

export {};

//const name; //error - const must have some value `while declaration/initialized`
// const name;

const name: string = 'Dinanath';
console.log('My name is : ' + name );

//error - const value is fixed, `not to change/re-assigned` in future
// const name: string = 'Dino';

4.2.5. let vs const

If variables have one time assignments (fixed value, not changed in future) use const
If value re-assignments/value updation requires use let
Const variables need value at the time of definition; const name='Dinanath';
Let variables can be defined/initialized with empty value; let name;
Const variables are immutable, not changeable variables
Let variables are mutable, can be changed or re-assigned

4.3. Type Annotations / Type System

JavaScript is not a typed language, However, TypeScript is a typed language, where we can specify the type of the variables, function parameters and object properties like a number, string, boolean, etc.
We can specify the type using : Type after the name of the variable, parameter or property, It is advisable to use annotation method to specify data type while declaring the variable (Example: let firstName: string = 'Dinanath')
Typescript does not allow to assign a different type of data to a variable
Type annotation method helps to eliminate any errors related to variable data type mismatch
The any data type is the supertype of all types in TypeScript which denotes a dynamic type

Advantage/Use of Type Annotations / Type System:

Static Type checking errors (Data type mismatch error)
Getting accurate intellisense help for specific data type (Example: specific data type variable will show only specific/related methods and properties etc.)

export {};

let isCompleted: boolean = false;
let id: number = 101;
let firstName: string = 'Dinanath';
let lastName: string = 'Jayaswal';

console.log(`User Details: ${firstName} ${lastName} ${isCompleted} ${id} `)

let fullName;
function showFullName(_fn: string ,_ln: string ) {
  let fullName = _fn + ' ' + _ln;
  console.log(`My FullName: ${fullName}`);
}

showFullName('Dino','Jas');

4.4. Data type `any`

Typescript introduced a new data type named any
A variable with any type can hold value with any data type (like the first variable holds string than assign number or boolean type)
For data type any there is no compile-time checking
The any data type is the supertype of all types in TypeScript which denotes a dynamic type

let data1:string = 'Data1'

//error - string type can not accept number or other data
// data1 = 50; 

// any data type variable can store any type of value, there are no data checking 
let data2:any = 'Data2';
data2 = 50;
data2 = true;
data2 = ['Hi','Hey','Good','Hello'];

console.log(data2);

4.5. Data type `array`

Arrays in Typescript works in the same way as they work in JavaScript
Same as JavaScript, TypeScript allows us to deal with arrays of values
There are two ways to write/declare an array:
1. let cities: string[];
  - let arrFrameworks: string [] = ['JavaScript','jQuery','Angular','React'];
2. let cities: Array<string>
  - let arrLanguages: Array<string> = ['C','C++','Java','Ruby','Phthon'];
  - In the above example, we declared an array of strings by assigning it the string type (Now TypeScript will make sure the array contains only strings)

export {};

let arrFrameworks: string [] = ['JavaScript','jQuery','Angular','React'];
console.log('arrFrameworks:',arrFrameworks);


let arrLanguages: Array<string> = ['C','C++','Java','Ruby','Phthon'];
console.log('arrLanguages',arrLanguages);

4.6. Tuples

Typescript provides a new special type of array called Tuples which can store multiple data types based values
Tuples represent a heterogeneous collection of values (multiple types of values in one collection/collection of values of various types)
Tuples enable storing multiple fields of different types
let personDetail: [string, number] = ['Dinanath', 35];

export {};

let arrFrameworksDetails:  [string,number] = ['JavaScript',7.0];
console.log('arrFrameworksDetails:',arrFrameworksDetails);

console.log('arrFramework Name:',arrFrameworksDetails[0]);
console.log('arrFramework version:',arrFrameworksDetails[1]);

4.7. Enumeration

Enums are used to define a set of named constants which can be used to document intent or to create a set of different cases (collection of related values that can be numeric or string values)
Enums defined or start with enum variableName keyword
There are three types of enums:
1. Numeric enum (number-based enums i.e. they store string values as numbers)
2. String enum (initialized with string values)
3. Heterogeneous enum (contain both string and numeric values)

export {};

enum RGBColor { Red, Green, Blue };
console.log('RGBColor:', RGBColor);
console.log('RGBColor.Green:', RGBColor.Green);

let colorBlue: RGBColor = RGBColor.Blue;
console.log('colorBlue:', colorBlue);

enum Cities1 { Mumbai = 10, Delhi = 20, Kolkata = 30, Chennai = 40, Bangalore = 50 }
console.log('Cities:', Cities1);
console.log('Bangalore:',Cities1.Bangalore);

enum Cities2 { Mumbai = 'M', Delhi = 'D', Kolkata = 'K', Chennai = 'C', Bangalore = 'B' }
console.log('Cities:', Cities2);
console.log('Bangalore:',Cities2.Bangalore);

4.8. Type Inference

Defining variable type is optional, but sometimes Typescript infer or decide the type of variable while initialization only
let details; // no type infer or decided/finalized as no value provided
let details = 'Human'; // string (hover on variable-details to know/get data type)
Once the data type is inferred or finalized by Typescript we cant assign other type values to it (will get an error not assignable)
Types are inferred by TypeScript compiler when:
- Variables are initialized
- Default values are set for parameters
- Function return types are determined

export {};

let details; //data type not infered
console.log('type of details:', typeof(details));

let cityName = 'Human'; // hover on cityName to check type details let cityName: string
console.log('type of cityName:', typeof(cityName));

//Error - Type '90' is not assignable to type 'string'.ts(2322), cant assign number to string data type
//cityName = 90

4.9. Type Assertion (Type Casting)

Type assertion allows Programmer to set the type of a value and tell the compiler not to infer
Type assertion can be used when Programmer have a better understanding of the type of a variable (we may know a more accurate type) than what TypeScript can infer
Type Assertion is similar to type casting in other languages
as keyword is used for Type Assertion, or before value specify the type

export {};

let id = 100;
let employeeID = &lt;number&gt; id;

let name = 'Dinanath';
let fName = 'Dinanath';
console.log('fName data type:',typeof(fName));

fName = fName as string;
console.log('fName data type:',typeof(fName));

4.10. Functions

Functions are the primary fundamental building block in JavaScript
A function is a set of statements to perform a specific task
Functions make the code more readable, maintainable, and reusable
Typescript functions help to specify the data type of function parameters as well as a function return type
In JavaScript every parameter is assumed to be required if no parameter passed - throws an error
With Typescript, we can denote/mark/treat parameter optional by adding ? question mark symbol
ES6 allows function parameters to have/specify simple and intuitive default values
It simply means that if no arguments are provided to function call these default parameters values will be used

export {};

// specify data types of parameters
function sum(num1: number, num2: number) {
  console.log(num1 + num2);
}

sum(10, 20);

//error - only numbers allowed
// sum('one','two');

// specify data types of parameters as well function return type
function showGreetings(message: string): string {
  return message;
}
let message1 = showGreetings('Welcome to Typescript');
console.log(message1);

export { };

// specify data types of parameters, use ? to denote optional parameters 
function sum(num1: number, num2?: number) {
  if (num2) {
    console.log(num1 + num2);
  } else {
    console.log(num1);
  }
}

sum(10, 20);
sum(100);

export { };

// specify data types of parameters, use ? to denote optional parameters, one can also specify default values
function sum(num1: number, num2: number = 50) {
  console.log(num1 + num2);
}

sum(10, 20);
sum(100);

4.11. Interface

Interfaces are the most flexible way to define the type of variables or properties of an object
The interface keyword is used to declare an interface
The interface is a structural/syntactical contract that defines the types, contract (rule) in your application
It defines the types and syntax for classes to follow, Classes derived from an interface must follow the structure provided by their interface
Any optional property defined in an interface are represented with ? question mark sign (city?: string)

export {};

interface Person {
  firstName: string;
  lastName: string;
  age?: number
}

function showDetails (_person: Person) {
  console.log(`Person Details: ${_person.firstName} ${_person.lastName} ${_person.age}`); 
}

let person1 = { 
  firstName: 'Dinanath',
  lastName: 'Jayaswal',
}

showDetails(person1);

let person2 = { 
  firstName: 'Dino',
  lastName: 'J.',
  age: 40
}

showDetails(person2);

4.12. Class constructor

TypeScript is object-oriented JavaScript
In OOPS (Object Oriented Programming Structure) a class is a blueprint for creating objects
JavaScript has been primarily a functional programming language works mainly on prototype-based inheritance, Functions are used to build reusable components
TypeScript introduced classes to avail the benefit of object-oriented techniques like interfaces, inheritance, encapsulation, and abstraction
Typescript helps to write constructors with shorter syntax, prefix parameters with access modifiers
Class-based inheritance needs extends keyword and main class properties and method can be accessed with super keyword

export {};

class Greetings {
  personName: string;

  constructor(name: string) {
    this.personName = name;
  }

  showGreet() {
    console.log(`Welcome, have a great Day ${this.personName}!`)
  }

}

let person1 = new Greetings('Dinanath');
console.log('person1.personName:',person1.personName);
person1.showGreet();

// class-based inheritance
class Person extends Greetings {

  constructor (pName: string) {
    super(pName);
  }

  doTask() {
    console.log('Person doing some task');
  }

}

let person1 = new Person('Sagar');
console.log('person1.name:',person1.name);
person1.showGreet();
person1.doTask();

4.13. Access Modifiers

Access modifiers are keywords that set the accessibility/availability/visibility of properties and methods
There are three types of access modifiers in TypeScript:
1. public -
  - A public data member has universal accessibility, Data members in a class are public by default
  - By default, all members of a class in TypeScript are public
  - All the public members can be accessed anywhere without any restrictions
2. private -
  - The private access modifier ensures that class members are visible only to that class and are not accessible outside the containing class
  - In case An external class member tries to access a private member, the compiler throws an error
3. protected -
  - The protected access modifier is similar to the private access modifier, except that protected members can be accessed using their deriving classes
  - A protected data member is accessible by the members within the same class as that of the former and also by the members of the child classes

export {};

class Greetings {
  public name: string;
  private privateName: string;
  protected protectedName: string;

  constructor(_name: string) {
    this.name = _name;
  }

  showGreet() {
    console.log(`Welcome, have a great Day ${this.name}!`)
  }

}

let greet1 = new Greetings('Dinanath');
console.log('greet1.name:',greet1.name);
greet1.showGreet();

// error - private property/variable not available outside
// console.log(greet1.privateName);

console.log(`// ------------------------------`);

// class-based inheritance
class Person extends Greetings {

  constructor (pName: string) {
    super(pName);
  }

  doTask() {
    console.log('Person doing some task');
    // error - private property/variable not available outside
    // console.log(greet1.privateName);

    // protected property/variable can be accessed in derived/child class
    console.log('this.protectedName:',this.protectedName);
  }

}

let person1 = new Person('Sagar');
console.log('person1.name:',person1.name);
person1.showGreet();
person1.doTask();

4.14. Decorator

Decorators are experimental features in Typescript and may not be part of feature releases
Decorators are a special type of declarations, metadata attached to classes, methods, and properties
Decorators use the form @expression, where expression must evaluate to a function that will be called at runtime with information about the decorated declaration
To enable experimental support for decorators, enable the experimentalDecorators compiler option either on the command line or in tsconfig.json:
command line: tsc --target ES5 --experimentalDecorators
tsconfig.json:

{
    "compilerOptions": {
        "target": "ES5",
        "experimentalDecorators": true
    }
}

Decorators begins with @ (at the rate sign)

@Component({
  selector: 'user',
  templateUrl: 'user.component.html',
  styleUrls: ['user.component.scss']
})

Section 5. Reference

5.1. Websites / Blogs

Official website: http://www.typescriptlang.org/
Source code: https://github.com/Microsoft/TypeScript

5.2. Books

https://livebook.manning.com/#!/book/typescript-quickly/chapter-1/v-5/1

Section 6. What's Next Step?

Many Congratulations! You have done it. Thank you for joining me for Typescript fundamentals for beginners. I hope you will start checking/testing and incorporating these features into your code right away. I hope now you have a solid understanding of Typescript new features and usability. Your next step could be looking into Typescript documentation. Now you are fully up to date and set to start with any latest javascript framework/library like Angular, React, Node, Vue.

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