Typescript

Question 1

TypeScript

Answer 1

TypeScript extends JavaScript by adding types to the language.

TypeScript is an open-source programming language developed and maintained by Microsoft. It is a strict syntactical superset of JavaScript and adds optional static typing to the language. TypeScript is designed for development of large applications and transcompiles to JavaScript.

Question 2

TypeScript vs JavaScript

Answer 2

TypeScript = JavaScript + Types + other stuffs

Types: type checking, type definition,…

TypeScript is superset of JavaScript

Question 3

Why TypeScript?

Answer 3

Makes building these complex apps more manageable

Framework like angular 2 using it

Question 4

Why need Node.js in Typescript

Answer 4

Node.js compile Typescript to Javascript

Run Javascript on Node.js

Question 5

Typescript array

Answer 5

var myarr : number[];
myarr =[];
myarr=[1,2];
myarr.push(1);
myarr.push(''); // error
var a:number = myarr.pop();

Question 6

If there is an error in TypeScript Compiler, will compiled js file be created?

Answer 6

Yes.

The error is only used for

Question 7

TypeScript vs JavaScript in action

Answer 7

• Type restrict in TypeScript

- In JS, there is no restriction in function types or number of arguments but there is in TypeScript

Question 8

TypeScript function

Answer 8

• Can use JS to define a function

- Restrict number of augments input and augment types

Question 9

Optional augments in TypeScript function

Answer 9

function add (a, b, c=0) {
    return a + b + c;
}

function add (a, b, c?) {
    return a + b + c;
}

function add (a, b?, c) { // not valid
    return a + b + c;
}

Question 10

Implicit typing

Answer 10

var a = 10; // TS automatically apply type number to a
var b = true; // TS automatically apply type boolean to a
var c = "Hello"; // TS automatically apply type string to a

Question 11

Implicit typing

Answer 11

var a = 10; // TS automatically apply type number to a
var b = true; // TS automatically apply type boolean to b
var c = "Hello"; // TS automatically apply type string to c

function greeting() : string {
    return "Hello";
}

var hello = greeting(); // TS automatically apply type string to hello

Notes:
- Has to be on the same line variable and assigned value

Question 12

Type any in TS

Answer 12

var a;
var a: any;

a = 10;
a = true;
a = "String";

-> Use to migrate JS to TS

Question 13

Union Type

Answer 13

var a : boolean | number;

a = 10;
a = true;
a = "String"; --> Error