TypeScript create new instance from class in a static context

Question

Is there a way in TypeScript to create new instances from a static method in a generic way?

I want to do something like:

class Base {
    static getInstance() {
         return new self(); // i need this line :)
    }
}

class Test extends Base {
}

class NextTest extends Base {
}

var test = Test.getInstance();
assert(test instanceof Test).toBe(true);

var nextTest = NextTest.getInstance();
assert(nextTest instanceof NextTest).toBe(true);

It would be really helpful if someone did something like this before and could help me. Maybe there is a JavaScript way?

Thanks in advance.

I am going to build TypeScript Models with an integrated RESTful Client. So you can import TestModel and call TestModel.objects.all() which needs to return a TestModel :D Somehow the objects class (actually it is the REST client) needs to know which Model to populate. — inferno
– inferno, Commented Apr 16, 2015 at 22:16

vasa_c · Accepted Answer · 2015-04-16 20:36:25Z

17

Hack :)

static getInstance() {
     return new this;
}

answered Apr 16, 2015 at 20:36

vasa_c

1,0142 gold badges12 silver badges18 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

inferno Over a year ago

Thanks for this.. I always tried my approach with a static property not with a method :D Similar to: "static prop: Manager = new Manager(new this);" - Which is not compiling :) I will go with a static method

ForrestLyman Over a year ago

When I try this I get the following error: error TS2351: Cannot use 'new' with an expression whose type lacks a call or construct signature.

lucaswxp Over a year ago

How one calls super? Doesn't work because I get the wrong type.

Anmol Saraf · Accepted Answer · 2017-02-13 06:27:24Z

-4

You can also use class name itself which in your example is Base,

static getInstance() {
   return new Base()
}

Another example is below which uses Greeter class name inside static function called createInstance, you can test following example at TypeScript Playground

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

    static createInstance(message: any) {
        return new Greeter(message);
    }
}

let greeter = Greeter.createInstance("world");

let button = document.createElement('button');
button.textContent = "Say Hello";
button.onclick = function() {
    alert(greeter.greet());
}

document.body.appendChild(button);

Hope it helps.

answered Feb 13, 2017 at 6:27

Anmol Saraf

15.9k10 gold badges55 silver badges61 bronze badges

2 Comments

mrm Over a year ago

This was answered correctly 2 years ago. Your answer does not return subclasses as per the question.

Anmol Saraf Over a year ago

Thanks for the update @mrm . Didn't notice about the sub classes requirement above. I was just trying out different codes and found an example with the Base class instead of 'this', just wanted to elaborate about using classname instead of this which also works if sub classing requirement isn't there, though haven't tested it out but I'll believe what you are saying as you already have tested it out. Thanks for pointing it out, helps the other users.

Collectives™ on Stack Overflow

TypeScript create new instance from class in a static context

2 Answers 2

3 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related