Generating a fresh instance of a class that mirrors an already existing instance, all without relying on eval()

Question

Generating a fresh instance of a class that mirrors an already existing instance, all without relying on eval()

I have an object named uniqueObject of an unspecified class and I am in need of creating a duplicate object from the same class. Here's my current approach:

I extract the class name using uniqueObject.constructor.name.
Then, I generate a new object of the same class using
```
eval(`new ${uniqueObject.constructor.name}()`)
```
.

The current code snippet functions without issues:

class classA { name = "Albert";}
class classB { name = "Isaac";}

let uniqueObject = new classA();

// later in the code, the constructor of uniqueObject is unknown
let extractedConstructorName = uniqueObject.constructor.name
let duplicatedObjectOfSameClass = eval(`new ${extractedConstructorName}()`);
console.log(duplicatedObjectOfSameClass .name); // "Albert"

However, I would like to avoid using eval(). Is there a more elegant solution?

(I am unable to utilize window[extractedConstructorName] as this code will not be executed in a web browser under normal circumstances. (I am unsure if it would even function in a browser.))

javascript typescript constructor eval

Answer 1

Answer №1

In the case that you are utilizing TypeScript, as demonstrated in this code snippet

class exampleClass_A { name = "Archimedes";}

I have crafted a demonstration for you:

class exampleClass_A { name = "Archimedes";}
class exampleClass_B { name = "Pythagoras";}

let exampleInstance = new exampleClass_A();

// subsequently, in another section of the code, the constructor of exampleInstance becomes unknown
//let constructorName = exampleInstance.constructor.name;
//let newInstanceOfTheSameClass = eval(`new ${constructorName}()`); // how can this be accomplished without eval()???

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

https://jsfiddle.net/t9gdasur/

Kindly inform me if it is effective. If not, I will attempt an alternative approach.

Answer 2

In the case that you are utilizing TypeScript, as demonstrated in this code snippet

class exampleClass_A { name = "Archimedes";}

I have crafted a demonstration for you:

class exampleClass_A { name = "Archimedes";}
class exampleClass_B { name = "Pythagoras";}

let exampleInstance = new exampleClass_A();

// subsequently, in another section of the code, the constructor of exampleInstance becomes unknown
//let constructorName = exampleInstance.constructor.name;
//let newInstanceOfTheSameClass = eval(`new ${constructorName}()`); // how can this be accomplished without eval()???

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

https://jsfiddle.net/t9gdasur/

Kindly inform me if it is effective. If not, I will attempt an alternative approach.

Answer 3

Answer №2

Directly invoke the constructor!

const duplicateInstance = new (sampleInstance.constructor as any)();
console.log(duplicateInstance);

The potential downside is that the constructor is not typed, so you will need to perform a cast and the returned value will lack typing.

Playground

Answer 4

Directly invoke the constructor!

const duplicateInstance = new (sampleInstance.constructor as any)();
console.log(duplicateInstance);

The potential downside is that the constructor is not typed, so you will need to perform a cast and the returned value will lack typing.

Playground

Answer 5

Answer №3

1- Obtain the reference to the constructor function of the current instance by accessing its prototype.

2- Utilize the retrieved constructor to generate a fresh instance of the identical class.

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

let sampleInstance = new sampleClass_A();

// Step 1: Obtain the constructor
const constructor = sampleInstance.__proto__.constructor;

// Step 2: Generate a new instance
let newInstanceOfTheSameClass = new constructor();

console.log(newInstanceOfTheSameClass.name); // "Archimedes"

Answer 6

1- Obtain the reference to the constructor function of the current instance by accessing its prototype.

2- Utilize the retrieved constructor to generate a fresh instance of the identical class.

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

let sampleInstance = new sampleClass_A();

// Step 1: Obtain the constructor
const constructor = sampleInstance.__proto__.constructor;

// Step 2: Generate a new instance
let newInstanceOfTheSameClass = new constructor();

console.log(newInstanceOfTheSameClass.name); // "Archimedes"

Generating a fresh instance of a class that mirrors an already existing instance, all without relying on eval()

Answer №1

Answer №2

Answer №3

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