Day 8 : TypeScript

Basic Concepts in TypeScript:

Variable declaration :

• The default or traditional declaration of variable is :

var a : number = 10;

• The let and const are two new concepts in variable declaration.
• The let keyword is some what same as var keyword.
• The let keyword allows user to avoid some of "gotchas" that we use in JS.
• Now, you all wondering what is "gotchas"??

                Gotchas are nothing but some what errors which we can avoid for better output. Consider a loop as an example :

//var keyword gives access to i outside loop.

//code: 

               for(var i=0;i<5;i++) {

                   console.log(i);

              }

              console.log(i);

//output:

0

1

2

3

4

5

//let keyword not gives access to i outside loop.

//code :

                    for(let i=0;i<5;i++) {

                       console.log(i);

              }        

                   console.log(i);

//output :

Error : Cannot found i

• So from above eg. we can say that, variables declared with let keyword cannot accessed outside block.
• The const keyword prevents the reassignments of variables.

Creating a class :

• In general, class is a blueprint of object.
• We can say that, class contains a group or collection of objects having common properties.
• Class contains or encapsulates data for objects.
• Syntax :

class class_name {

.......

//class scope

                                                                      } 

Creating a object :

• Object is a instance of a class.
• Object is a real-world and run-time entity.
• Object is a entity that have state(data) and behavior(functionality).
• Syntax :

var object_name = new class_name();

Import :

• For using or accessing a already written program or module we use import statement.
• Syntax :

import { export file_name } from "file path without extension"

• Eg :

Export :

• The export is used as a prefix for variable or class which we want to access in other module or program.
• Eg :

Tsconfig file :

• The tsconfig.json file indicates the root directory of TypeScript.
• The tsconfig.json file specifies the root files as well as the compiler options for compiling a program.
• As we run tsc command for each .ts file for converting it into .js file. The tsconfig.json file converts the all .ts file into .js and make our work easy.
• For tsconfig.json file run following command on terminal :

> tsc --init

• The above command automatically creates a tsconfig.json file.

• We can use a "outDir" for creating a new folder which having the .js files of our module, as i created in above image.

Thank You!!!

For more understanding watch below video :

Angular

JavaScript Day 1 : Day 1

JavaScript Day 2 Global Pollution : Day 2 Global

JavaScript Day 2  Undefined and Hoisting : Day 2 Undefined

JavaScript Day 3 : Day 3

JavaScript Day 4 : Day 4

JavaScript Day 5 : Day 5

JavaScript Day 6 : Day 6

TypeScript Day 7 : Day 7