TypeScript - Classes

TypeScript is object oriented JavaScript. TypeScript supports object-oriented programming features like classes, interfaces, etc. A class in terms of OOP is a blueprint for creating objects. A class encapsulates data for the object. Typescript gives built in support for this concept called class. JavaScript ES5 or earlier didn’t support classes. Typescript gets this feature from ES6.

TypeScript - Overview

JavaScript was introduced as a language for the client side. The development of Node.js has marked JavaScript as an emerging server-side technology too. However, as JavaScript code grows, it tends to get messier, making it difficult to maintain and reuse the code.

TypeScript - Environment Setup

Try it Option Online

We already have set up TypeScript programming online, so that you can execute all the available examples online at the same time when you are doing your theory work. This gives you confidence in what you are reading and to check the result with different options. Feel free to modify any example and execute it online.

TypeScript - Basic Syntax

Syntax defines a set of rules for writing programs. Every language specification defines its own syntax. A TypeScript program is composed of −

• Modules
• Functions
• Variables
• Statements and Expressions
• Comments

TypeScript - Types

The Type System represents the different types of values supported by the language. The Type System checks the validity of the supplied values, before they are stored or manipulated by the program. This ensures that the code behaves as expected. The Type System further allows for richer code hinting and automated documentation too.

TypeScript - Variables

A variable, by definition, is “a named space in the memory” that stores values. In other words, it acts as a container for values in a program. TypeScript variables must follow the JavaScript naming rules −

• Variable names can contain alphabets and numeric digits.
• They cannot contain spaces and special characters, except the underscore (_) and the dollar ($) sign.
• Variable names cannot begin with a digit.
  

TypeScript - Operators

What is an Operator?

An operator defines some function that will be performed on the data. The data on which operators work are called operands. Consider the following expression −
7 + 5 = 12
Here, the values 7, 5, and 12 are operands, while + and = are operators.
The major operators in TypeScript can be classified as −

TypeScript - Decision Making

Decision-making structures require that the programmer specifies one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

TypeScript - Loops

You may encounter situations, when a block of code needs to be executed several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

TypeScript - Functions

Functions are the building blocks of readable, maintainable, and reusable code. A function is a set of statements to perform a specific task. Functions organize the program into logical blocks of code. Once defined, functions may be called to access code. This makes the code reusable. Moreover, functions make it easy to read and maintain the program’s code.

TypeScript - Numbers

TypeScript like JavaScript supports numeric values as Number objects. A number object converts numeric literal to an instance of the number class. The Number class acts as a wrapper and enables manipulation of numeric literals as they were objects.

TypeScript - Strings

The String object lets you work with a series of characters. It wraps the string primitive data type with a number of helper methods.

TypeScript - Arrays

The use of variables to store values poses the following limitations −

• Variables are scalar in nature. In other words, a variable declaration can only contain a single at a time. This means that to store n values in a program n variable declarations will be needed. Hence, the use of variables is not feasible when one needs to store a larger collection of values.
  

TypeScript - Tuples

At times, there might be a need to store a collection of values of varied types. Arrays will not serve this purpose. TypeScript gives us a data type called tuple that helps to achieve such a purpose.
It represents a heterogeneous collection of values. In other words, tuples enable storing multiple fields of different types. Tuples can also be passed as parameters to functions.

TypeScript - Union

TypeScript 1.4 gives programs the ability to combine one or two types. Union types are a powerful way to express a value that can be one of the several types. Two or more data types are combined using the pipe symbol (|) to denote a Union Type. In other words, a union type is written as a sequence of types separated by vertical bars.

TypeScript - Interfaces

An interface is a syntactical contract that an entity should conform to. In other words, an interface defines the syntax that any entity must adhere to.
Interfaces define properties, methods, and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the

TypeScript - Objects

An object is an instance which contains set of key value pairs. The values can be scalar values or functions or even array of other objects. The syntax is given below −

Syntax

var object_name = { 
   key1: “value1”, //scalar value 
   key2: “value”,  
   key3: function() {
      //functions 

TypeScript - Namespaces

A namespace is a way to logically group related code. This is inbuilt into TypeScript unlike in JavaScript where variables declarations go into a global scope and if multiple JavaScript files are used within same project there will be possibility of overwriting or misconstruing the same variables, which will lead to the “global namespace pollution problem” in JavaScript.

TypeScript - Modules

A module is designed with the idea to organize code written in TypeScript. Modules are broadly divided into −

• Internal Modules
• External Modules

TypeScript - Ambients

Ambient declarations are a way of telling the TypeScript compiler that the actual source code exists elsewhere. When you are consuming a bunch of third party js libraries like jquery/angularjs/nodejs you can’t rewrite it in TypeScript.