a reference to the constructor function

Question

How can I get reference to the constructor function for any object in typescript?

Example in JavaScript:

var anyObject = new this.constructor(options);

or

var anyObject = new someObj.constructor(options);

or

class Greeter { 
  greeting: string; 
  constructor(message: string, options: any) { 
       this.options = options; 
       this.greeting = message; 
  } greet() { 
     return "Hello, " + this.greeting; 
  } createAnyObj(){  
     return new this.constructor(this.options); 
  } 
} 

 var t= new Greeter('mes',{param1: 'val1'});
 var b=t.createAnyObj();

Thanks.

More examples:

>>>Link to typescript playground

what is the purpose of createAnyObj method? what does it expected to return? — Rajeesh
– Rajeesh, Commented Feb 12, 2013 at 7:03

Fenton · Accepted Answer · 2013-02-12 10:27:55Z

2

You could achieve what you need using the following code:

class A {
    constructor(public options: any) {

    }

    duplicate() {
        return new A(this.options);
    }

    someMethod() {
        return 'Hello! I am class A!';
    }
}

class B extends A {
    constructor(options: any) {
        super(options);
    }

    someMethod() {
        return 'This is class B!';
    }

    duplicate() : A {
        return new B(this.options);
    }
}

var objA = new A({key1: 'value1'});
var objWhithOptionsObjA = objA.duplicate(); //=> Instaceof class A
alert(objWhithOptionsObjA.someMethod());

var objB = new B({key2: 'value2'});
var objWhithOptionsObjB = objB.duplicate(); //=> Instaceof class B
alert(objWhithOptionsObjB.someMethod());

You need a constructor on B that just passes options to the super class. You override the duplicate method to return a B, which is a sub-type of A.

answered Feb 12, 2013 at 10:27

Fenton

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2 Comments

mantsevich Over a year ago

if I need to inherit from a class B to C, class C to class D, class D to a class E...? It is not easy and need a lot of dublicate code...

Fenton Over a year ago

When Generics arrive in TypeScript you could potentially use that to reduce the duplication. That is scheduled for 0.9.0.

mantsevich · Accepted Answer · 2013-02-14 05:17:20Z

This problem was solved with next solution:

module Example{
    // Thank you, JavaScript!
    export function getConstructor(obj){
        return obj.constructor;
    }
    export class A{
        constructor(private options: any){}
        dublicate(){
            return new (getConstructor(this))(this.options);
        }
        someMethod(){
            return 'This is class A';
        }
    }
    export class B extends A{
        someMethod(){
            return 'This is class B';
        }
    }
}

// Class A
var objA = new Example.A({key1: 'val1'});
console.log(objA.someMethod(), objA); //=> This is class A
var objA2 = objA.dublicate();
console.log(objA2.someMethod(), objA2); //=> This is class A

// Class B
var objB = new Example.B({key2: 'val2'});
console.log(objB.someMethod(), objB); //=> This is class B
var objB2 = objB.dublicate();
console.log(objB2.someMethod(), objB2); //=> This is class B

Live example => Open playground

Rajeesh · Accepted Answer · 2013-02-12 08:49:55Z

0

Use the new operator to instantiate the object with the required parameter in the constructor. This is similar to how you do it in other Object Oriented programming languages, below is an example from the typescript official website

class Greeter {
    constructor(public message: string, public options?: any) {          
     }

     greet() {
      return "Hello, " + this.message;
     }

     createAnyObj(){  
        return new Greeter(this.message, this.options);         
     } 
}

var greeter = new Greeter("world");

edited Feb 12, 2013 at 8:49

answered Feb 12, 2013 at 6:50

Rajeesh

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6 Comments

mantsevich Over a year ago

example: class Greeter { greeting: string; constructor(message: string, options: any) { this.options = options; this.greeting = message; } greet() { return "Hello, " + this.greeting; } createAnyObj(){ return new this.constructor(this.options); } }

Rajeesh Over a year ago

why you need to create any other objects(createAnyObj) other than Greeter inside the class? what object type you are expecting to return from that method?

mantsevich Over a year ago

I add more examples. See link. Thanks.

Rajeesh Over a year ago

Please see the sample example in TypeScript playground - tinyurl.com/c7cxn5w . I have also update my answer to your latest updates

mantsevich Over a year ago

This solution is not suitable, because the object [objWhithOptionsObjB] instanceof [class A]. This is error! example: objWhithOptionsObjB.someMethod(); => 'Hello! I am class A!'.

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