Interview Questions.

Question 1. What Is Typescript And Why Do We Need It?

Answer :

JavaScript is the only purchaser aspect language universally supported by way of all browsers. But JavaScript isn't the first-rate designed language. It’s no longer a class-based totally object-orientated language, doesn’t guide magnificence primarily based inheritance, unreliable dynamic typing and lacks in assemble time blunders checking. And TypeScript addresses a lot of these problems. In other words, TypeScript is an attempt to “repair” JavaScript troubles.

TypeScript is a unfastened and open source programming language developed and maintained by using Microsoft. It is a strict superset of JavaScript, and provides optionally available static typing and class-based totally object-oriented programming to the language. TypeScript is pretty clean to analyze and use for builders acquainted with C#, Java and all robust typed languages. At the give up of day “TypeScript is a language that generates simple JavaScript files.”

As said on Typescript legitimate website, “TypeScript helps you to write JavaScript the manner you really need to. TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. Any browser. Any host. Any OS. Open Source.” Where “typed” means that it considers the sorts of variables, parameters and features.

Question 2. What Are The Benefits Of Typescript?

Answer :

TypeScript has following blessings:

It facilitates in code structuring
Use class primarily based object oriented programming
Impose coding guidelines
Offers kind checking
Compile time mistakes checking
Intellisense
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Question three. What Are Different Components Of Typescript?

Answer :

There are in particular three additives of TypeScript:

Language – The maximum crucial element for builders is the brand new language. The language consists of recent syntax, key phrases and allows you to put in writing TypeScript.
Compiler – The TypeScript compiler is open source, move-platform and open specification, and is written in TypeScript. Compiler will assemble your TypeScript into JavaScript. And it's going to additionally emit errors, if any. It can also help in concatenating specific documents to a single output report and in generating supply maps.
Language Service – TypeScript language service which powers the interactive TypeScript enjoy in Visual Studio, VS Code, Sublime, the TypeScript playground and different editor.
Question 4. How Can You Get Typescript And Install It?

Answer :

TypeScript can be set up and managed through npm, the Node.Js package supervisor. To set up TypeScript, first ensure the npm is mounted well. And then run the subsequent command to put in TypeScript globally to your gadget.

Npm install -g typescript

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Question five. How Do You Compile Typescript Files?

Answer :

The extension for any TypeScript report is “.Ts”. And any JavaScript report is TypeScript report as it's miles a superset of JavaScript. So exchange extension of “.Js” to “.Ts” document and your TypeScript document is prepared. To assemble any .Ts file into .Js, use the subsequent command.

Tsc <TypeScript File Name>

For instance, to assemble “Helloworld.Ts”:

tsc helloworld.Ts

And the result might be helloworld.Js.

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Question 6. Is It Possible To Compile .Ts Automatically With Real Time Changes In .Ts File?

Answer :

Yes. Using --watch compiler alternative, this could be achieved.

Tsc --watch file1.Ts

This will first bring together file1.Ts in document.Js and look ahead to the file modifications. As soon as there is any trade detected, it will collect it again. But you need to ensure that command spark off should no longer be closed, used with --watchoption.

Question 7. Does Typescript Support All Object Oriented Principles?

Answer :

YES. There are four main standards to Object Oriented Programming: Encapsulation, Inheritance, Abstraction, and Polymorphism. TypeScript can put into effect all four of them with its smaller and cleaner syntax.

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Question eight. Which Object Oriented Terms Are Supported By Typescript?

Answer :

TypeScript supports the subsequent item oriented terms:

Modules
Classes
Interfaces
Data Types
Member capabilities
Question 9. Which Are The Different Data Types Supported By Typescript?

Answer :

TypeScript helps the following records types:

Boolean var bValue: boolean = fake;
Number var age: variety = 16;
String var name: string = "jon";
Array var listing:number[] = [1, 2, 3];
Enum
enum Color Red, Green, Blue;

var c: Color = Color.Green;

Any var unknownType: any = four;
Void
characteristic NoReturnType(): void 

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Question 10. How Typescript Is Optionally Statically Typed Language?

Answer :

TypeScript is referred as optionally statically typed, which means you can ask the compiler to ignore the type of a variable. Using any statistics type, we can assign any sort of value to the variable. TypeScript will now not deliver any blunders checking in the course of compilation.

Var unknownType: any = 4;
unknownType = "Okay, I am a string";
unknownType = fake; // A boolean.

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Question eleven. What Are Modules In Typescript?

Answer :

Modules are the manner to prepare code in TypeScript. Modules don’t have any features, but can incorporate instructions and interfaces. It is same like namespace in C#.

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Question 12. What Are Classes In Typescript?

Answer :

The idea of training could be very similar to .NET/Java. A Class will have constructor, member variables, properties and techniques. TypeScript also allows get entry to modifiers “non-public” and “public” for member variables and features.

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Question thirteen. How Do You Implement Inheritance In Typescript?

Answer :

Using extends keyword, we are able to put in force inheritance.

Elegance Animal 
    public domestic:boolean;
    constructor(public call: string)  

class Cat extends Animal 
    constructor(name: string, home: boolean) 
     
      excellent(call); 
      this.Domestic = real;
    

magnificence Tiger extends Animal 
    constructor(call: string, home: boolean) 
     
      extremely good(name); 
      this.Domestic = false;
    

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Question 14. How To Call Base Class Constructor From Child Class In Typescript?

Answer :

Using fantastic(), we can name base class constructor, as visible inside the above code.

Question 15. What Is The Default Access Modifier For Members Of A Class In Typescript?

Answer :

In TypeScript, each member of sophistication is public by default.

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Question sixteen. How Can You Allow Classes Defined In A Module To Be Accessible Outside Of The Module?

Answer :

Classed define in a module are available in the module. Outside the module, you can’t get admission to them.

Module Vehicle 
    elegance Car 
        constructor (
            public make: string, 
            public model: string)  
    
    var audiCar = new Car("Audi", "Q7");

// This may not work
var fordCar = Vehicle.Car("Ford", "Figo");

As in keeping with above code, fordCar variable will deliver us bring together time blunders. To make lessons accessible outside module, use export keyword for classes.

Module Vehicle 
    export class Car 
        constructor (
            public make: string, 
            public version: string)  
    
    var audiCar = new Car("Audi", "Q7");

// This works now
var fordCar = Vehicle.Car("Ford", "Figo");

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Question 17. How Does Typescript Support Optional Parameters In Function As In Javascript Every Parameter Is Optional For A Function?

Answer :

In JavaScript, each parameter is taken into consideration elective. If no fee is furnished, then it's far treated as undefined. So whilst writing features in TypeScript, we are able to make a parameter non-obligatory using the “?” after the parameter call.

Feature Demo(arg1: range, arg2? :range) 

So, arg1 is usually required and arg2 is an elective parameter. Remember, optionally available parameters ought to follow required parameters. If we want to make arg1 non-compulsory, in preference to arg2, then we want to trade the order and arg1 need to be positioned after arg2.

Function Demo(arg2: wide variety, arg1? :quantity) 

Similar to non-compulsory parameters, default parameters are also supported.

Characteristic Demo(arg1: wide variety, arg2 = four) 

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Question 18. Does Typescript Support Function Overloading As Javascript Doesn’t Support Function Overloading?

Answer :

Yes, TypeScript does guide feature overloading. But the implementation is odd. When you overload in TypeScript, you simplest have one implementation with more than one signatures.

Magnificence Customer 
    call: string;
    Id: wide variety;

    upload(Id: range);
    upload(call:string);
    add(fee: any) 
    if (price && typeof price == "range") 
        //Do something
    
    if (price && typeof cost == "string") 
        //Do Something
    
   

The first signature has one parameter of kind range while the second signature has a parameter of type string. The 0.33 feature includes the actual implementation and has a parameter of type any. The any statistics kind can take any sort of records. The implementation then tests for the type of the furnished parameter and executes a one of a kind piece of code based totally on provider parameter type.

OR You can also use union kind introduced in TypeScript 1.4. Union kinds permit you to represent a value that is one of more than one kinds.

Upload(a:stringquantity) 
   //do some thing

Using union type, you can normally eliminate the want for an overload.

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Question 19. Is It Possible To Debug Any Typescript File?

Answer :

Yes, it's miles feasible. To debug it, you need .Js supply map report. If you are new to supply map, study more right here. So collect the .Ts report with the --sourcemap flag to generate a supply map document.

Tsc -sourcemap file1.Ts

This will create file1.Js and file1.Js.Map. And remaining line of file1.Js might be reference of source map file.

//# sourceMappingURL=file1.Js.Map

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Question 20. What Is Typescript Definition Manager And Why Do You Need It?

Answer :

TypeScript Definition Manager (TSD) is a bundle supervisor to go looking and deploy TypeScript definition documents directly from the community driven DefinitelyTyped repository. Let’s see with an example.

Suppose, you need to use some jQuery code for your .Ts report.

$(record).Equipped(function()  //Your jQuery code );

And now when you attempt to collect it using tsc, you'll get assemble time blunders Cannot locate call “$”. That’s because TypeScript can’t understand what does “$” manner. So somehow we want to inform TypeScript compiler that it belongs to jQuery. That’s in which TSD comes into play. You can down load jQuery Type Definition report and consist of it to your .Ts file. First, install TSD.

Npm installation tsd -g 

In your typescript listing, create a brand new typescript assignment with the aid of strolling:

tsd init

Then install the definition record for jquery.

Tsd query jquery --movement deploy

This will download and create a new listing containing your jquery definition file. The definition document ends with “.D.Ts”. So now encompass it through updating your typescript record to factor to the jquery definition.

///
$(document).Geared up(feature()  //To Do
);

Now try and compile again and this time, js will be generated with none blunders.

So TSD will help you to get type definition document for required framework. If you desire to use angular, then down load angular type definition document.

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Question 21. What Is Typescript Declare Keyword?

Answer :

It’s pretty viable that JavaScript libraries/frameworks don’t have TypeScript definition files and but you need to use them without any mistakes. Te solution is to apply the claim key-word. The declare key-word is used for ambient declarations wherein you want to define a variable that won't have originated from a TypeScript report.

Claim var unKnownLibrary;

Question 22. How To Generate Typescript Definition File From Any .Ts File?

Answer :

You can generate TypeScript definition record from any .Ts document via tsc compiler. Generating a TypeScript definition will make your TypeScript document reusable.

Tsc --declaration file1.Ts

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Question 23. What Is Tsconfig.Json File?

Answer :

The presence of a tsconfig.Json file in a listing shows that the listing is the root of a TypeScript assignment. The tsconfig.Json report specifies the root files and the compiler options required to collect the venture. And using this document, we can streamline building TypeScript assignment. Below is a pattern tsconfig.Json file.

   "compilerOptions": 
      "removeComments": authentic,
      "sourceMap": real
   ,
   "documents": [
      "main.Ts",
      "othermodule.Ts"
    ]

Within files section, outline all the .Ts files within the undertaking. And while you invoke tsc without any different arguments with the above record inside the cutting-edge listing, it will compile all the documents with the given compiler option settings.

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Question 24. What Are The Disadvantages Of Typescript?

Answer :

Well, TypeScript is remarkable however there are a few dangers as well.

TypeScript is just some other way to write JavaScript. It doesn’t restoration the problems of JavaScript. It simply creates an illusion that it does.
One extra tool to analyze.
TypeScript has dependency on kind definition files, if you wish to use any current JavaScript libraries.
Quality of type definition files is a problem as how will you be sure the definitions are correct?
Frequent releases of recent variations JavaScript library is also a ache place. Because if their kind definition files are not up to date then you could’t use them immediately.
In order to run the software inside the browser, a compile step is required to transform TypeScript into JavaScript.
Web developers are the use of JavaScript from a long time and TypeScript doesn’t deliver whatever new.
To use any third birthday party library, definition document is you want. And no longer all of the third celebration library have definition record to be had.
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