Typescript-101

Question 1

What is the diff b/w let, var & const?

Answer 1

Var will create a global variable and it is availabel in Global Object
Let will create a global variable, but does not belong to Global Object
Const will create a global Constant and it is not a property of Global Object

Question 2

What is the advantage of let?

Answer 2

With let you can create block level vars

Question 3

What is the advantage of const?

Answer 3

const requires intiallization and must not change while time

Question 4

Can we define objects with let

Answer 4

Yes

Question 5

Ca we define html templates with let

Answer 5

Yes A good way to do that

Question 6

How can you define template literals with let?

Answer 6

let obj = {
name : "kjskj
}"

let templateStr = “Name is” + $(obj.name)

Question 7

What is arrow function?

Answer 7

Arrow function is one way of writing inline function, like

var sum = (a,b) => { return a+b;}

var sum = (a,b) => a+b;

Question 8

Does Arrow function retains the Lexical scope of this?

Answer 8

YEs

Question 9

Write code for a class and constructor?

Answer 9

Class Person {
constructor(name) { // need not define the as var or let
this.name = name;
}

}

Question 10

Do you add access modifer or return type in function or construtors?

Answer 10

Nope straight to name

Question 11

How can you extend the class ?

Answer 11

Using keyword extends and use super where required

Question 12

How can we create an obj of a class?

Answer 12

let obj = new Employee(“sdfsfdee”);

Question 13

What is Object.create

Answer 13

To do prototypical inheritance without using constructor function

Question 14

What is the public access modifier?

Answer 14

Use export

Question 15

What is import do?

Answer 15

To import any exported entity

Question 16

How can you import everthing ?

Answer 16

import * as item from “./mod.js”

Question 17

Give one example of how the typesscript code looks in JS form?

Answer 17

class Greeter {
greeting : string;
constructor(message: string){
this.greeting: message;

}

greet(){

return “Greet”

}

let greeter = new Greeter(“Greeter”);

}

The above looks below in JS:

var Greeter = (function(){
      function Greeter(message){
               this.greeting = message;

}

Greeter.prototype.greet = function(){
return “Greet”;

}

return Greeter; // So i JS you can return the obj in the class itself as we do in JAVA

}());

Question 18

How do you define a String type in TS?

Answer 18

message: string;

Question 19

Do we require to specify the function keyword to start a function?

Answer 19

Need not

Question 20

How many Primitive types we have in TS?

Answer 20

string, Number, Boolean, undefined, null

Question 21

What all format des Number supports?

Answer 21

Float and int, also it supports Hexadecimal, Octal, decimal, binary

Question 22

How do you define the variable , variabetype , variablename & variablevalue?

Answer 22

let fName: string = ““myname””;

Question 23

What is the diff b/w null & undefined?

Answer 23

undefined means the value has not been defined, null means it has defined the object & that object is null.

Question 24

Do we have Array, Enum, Any & Void in TS

Answer 24

Yes we have

Question 25

How do you define an array

Answer 25

var listnum:number[] = [20,40];

Question 26

How do you make one Any type var ?

Answer 26

let me; Or var me;

Question 27

How do you define enums?

Answer 27

``` enum Cards{DIAMOND, SPADE}; var c = Cards.DIAMOND; c= 1;// Cards.DIAMOND; ```

Question 28

How can I define a function with a function keyword?

Answer 28

``` function getData(mesaage): void{ //do some } ```

Question 29

How do define an interface?

Answer 29

interface myInterface { greetUser(message: string): void; }

Question 30

How can we implement and interface?

Answer 30

``` class implClass implements myInterface { greetUser(msg: string){ ``` return "name"; } }

Question 31

How will you aceess the methods of a class?

Answer 31

``` function(greet: GreeterClass){ greet.greetUser("Hello"); } ```

Question 32

What is the default access modifer?

Answer 32

public

Question 33

Which keyword helps in instantiating a class?

Answer 33

new

Question 34

How can you define an anonymous function?

Answer 34

let myFunct = function(message: string) {return message};

Question 35

How can we pass a default value to a function argument?

Answer 35

function me(message: string ="hello"){ }