Creating new instance of the same class as an existing instance, without using eval()

Question

I have an instance sampleInstance of an unknown class and I need to create a second instance of the same class. Here's what I am doing right now:

1. I look up the class name with sampleInstance.constructor.name.
2. Next, I use eval(`new ${sampleInstance.constructor.name}()`) to create a new instance of the same class.

The code below works fine:

class sampleClass_A { name = "Archimedes";}
class sampleClass_B { name = "Pythagoras";}

let sampleInstance = new sampleClass_A();

// later, in another part of the code, I don't know the constructor of sampleInstance anymore
let constructorName = sampleInstance.constructor.name
let newInstanceOfTheSameClass = eval(`new ${constructorName}()`); // how to do without eval()???
console.log(newInstanceOfTheSameClass .name); // "Archimedes"

But I'd rather not use eval(). What's a cleaner alternative?

(I cannot use window[constructorName] because this code will not run in a browser in the general case. (Not even sure if it would work in a browser.))

Answer 1

Assuming you're using typescript, as seen in this instance code

class sampleClass_A { name = "Archimedes";}

I created a fiddle for you:

class sampleClass_A { name = "Archimedes";}
class sampleClass_B { name = "Pythagoras";}

let sampleInstance = new sampleClass_A();

// later, in another part of the code, I don't know the constructor of sampleInstance anymore
//let constructorName = sampleInstance.constructor.name;
//let newInstanceOfTheSameClass = eval(`new ${constructorName}()`); // how to do without eval()???

let newInstanceOfTheSameClass = new sampleInstance.constructor();
console.log(newInstanceOfTheSameClass .name); // "Archimedes"

https://jsfiddle.net/t9gdasur/

Let me know if it works. if not, I'll try something else.