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what is Difference between keyword new and :(colon) symbol while creating the new instance of a class

-1

I have 2 class i want to import one class in

Class students

export class students 
 public avr=123;
 constructor(a,b,c)

class college

import students from './commonwork'
export class college
 constructor(public abc:students)

This way works fine.

But

when I try to create the instance of class with new keyword in College class either in constructor or any where inside the class

var studentinstance= new student()

I get the error as "Expected 3 arguments, but got 0.ts(2554)"

Can some one please explain the difference creating the instance with new keyword and :(colon)

angular typescript

share|improve this question

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The colon doesn't create anything, that just specifies the type of the parameter. If there's a students in Angular's DI, it will inject it for you. When you try to new up a student, you indeed do not provide the arguments required. It's unclear what part of this outcome was unexpected.
  
  – jonrsharpe
  Mar 7 at 18:09
  
  

  
  
  
  

add a comment | 

-1

I have 2 class i want to import one class in

Class students

export class students 
 public avr=123;
 constructor(a,b,c)

class college

import students from './commonwork'
export class college
 constructor(public abc:students)

This way works fine.

But

when I try to create the instance of class with new keyword in College class either in constructor or any where inside the class

var studentinstance= new student()

I get the error as "Expected 3 arguments, but got 0.ts(2554)"

Can some one please explain the difference creating the instance with new keyword and :(colon)

angular typescript

share|improve this question

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The colon doesn't create anything, that just specifies the type of the parameter. If there's a students in Angular's DI, it will inject it for you. When you try to new up a student, you indeed do not provide the arguments required. It's unclear what part of this outcome was unexpected.
  
  – jonrsharpe
  Mar 7 at 18:09
  
  

  
  
  
  

add a comment | 

I have 2 class i want to import one class in

Class students

export class students 
 public avr=123;
 constructor(a,b,c)

class college

import students from './commonwork'
export class college
 constructor(public abc:students)

This way works fine.

But

when I try to create the instance of class with new keyword in College class either in constructor or any where inside the class

var studentinstance= new student()

I get the error as "Expected 3 arguments, but got 0.ts(2554)"

Can some one please explain the difference creating the instance with new keyword and :(colon)

angular typescript

share|improve this question

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

export class students 
 public avr=123;
 constructor(a,b,c)

import students from './commonwork'
export class college
 constructor(public abc:students)

var studentinstance= new student()

angular typescript

angular typescript

share|improve this question

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

share|improve this question

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

edited Mar 7 at 18:12

Heretic Monkey

6,55863672

asked Mar 7 at 18:07

AkkiAkki

31

asked Mar 7 at 18:07

AkkiAkki

31

2 Answers
2

active

oldest

votes

0

public abc:students doesn't create anything.¹ The :students part just assigns a type to abc. It doesn't create an instance of that type, it just says that if abc is going to refer to anything, it has to be of type students.

This:

var studentinstance= new student()

...is creating a variable (studentinstance) and assigning a student (singular) instance. The after it is not in any way connected to it, it's just an empty block following the statement which you can and should remove.

I suggest walking through some basic TypeScript tutorials.

---

¹ In the place it appears (the constructor parameter list), it declares abc as a property of the students instance and also as the first parameter to the constructor (and automatically sets the property from the constructor parameter). So in that sense you might say it creates a property. It doesn't create an object, however.

share|improve this answer

edited Mar 7 at 18:27

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

add a comment | 

0

: declares a type; it does not create an instance.

See the documentation.

share|improve this answer

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

add a comment | 

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0

public abc:students doesn't create anything.¹ The :students part just assigns a type to abc. It doesn't create an instance of that type, it just says that if abc is going to refer to anything, it has to be of type students.

This:

var studentinstance= new student()

...is creating a variable (studentinstance) and assigning a student (singular) instance. The after it is not in any way connected to it, it's just an empty block following the statement which you can and should remove.

I suggest walking through some basic TypeScript tutorials.

---

¹ In the place it appears (the constructor parameter list), it declares abc as a property of the students instance and also as the first parameter to the constructor (and automatically sets the property from the constructor parameter). So in that sense you might say it creates a property. It doesn't create an object, however.

share|improve this answer

edited Mar 7 at 18:27

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

add a comment | 

0

public abc:students doesn't create anything.¹ The :students part just assigns a type to abc. It doesn't create an instance of that type, it just says that if abc is going to refer to anything, it has to be of type students.

This:

var studentinstance= new student()

...is creating a variable (studentinstance) and assigning a student (singular) instance. The after it is not in any way connected to it, it's just an empty block following the statement which you can and should remove.

I suggest walking through some basic TypeScript tutorials.

---

¹ In the place it appears (the constructor parameter list), it declares abc as a property of the students instance and also as the first parameter to the constructor (and automatically sets the property from the constructor parameter). So in that sense you might say it creates a property. It doesn't create an object, however.

share|improve this answer

edited Mar 7 at 18:27

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

add a comment | 

public abc:students doesn't create anything.¹ The :students part just assigns a type to abc. It doesn't create an instance of that type, it just says that if abc is going to refer to anything, it has to be of type students.

This:

var studentinstance= new student()

...is creating a variable (studentinstance) and assigning a student (singular) instance. The after it is not in any way connected to it, it's just an empty block following the statement which you can and should remove.

I suggest walking through some basic TypeScript tutorials.

---

¹ In the place it appears (the constructor parameter list), it declares abc as a property of the students instance and also as the first parameter to the constructor (and automatically sets the property from the constructor parameter). So in that sense you might say it creates a property. It doesn't create an object, however.

share|improve this answer

edited Mar 7 at 18:27

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

var studentinstance= new student()

share|improve this answer

edited Mar 7 at 18:27

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

answered Mar 7 at 18:10

T.J. CrowderT.J. Crowder

697k12312401336

0

: declares a type; it does not create an instance.

See the documentation.

share|improve this answer

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

add a comment | 

0

: declares a type; it does not create an instance.

See the documentation.

share|improve this answer

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

add a comment | 

: declares a type; it does not create an instance.

See the documentation.

share|improve this answer

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

share|improve this answer

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770

answered Mar 7 at 18:09

SLaksSLaks

692k13916501770