Determine the data type of parameters in TypeScript

I'm currently working on creating a function that takes a class (Clazz) as a parameter and returns an instance of the same class, like this:

function createInstance(Clazz) {
    ...
    return new Clazz();
}

Is there a way to automatically determine the type of Clazz and use it as the return type for this function? I know that I can achieve this with generics like this:

function createInstance<T>(Clazz: new () => T): T {
    ...
    return new Clazz();
}

var instance = createInstance<myClass>(myClass)

However, I want to avoid repeating myClass as shown in the example above.

Answer №1

A simple solution would be to eliminate the <myClass> and everything will work smoothly:

function myFunction<T>(Clazz: new () => T): T {
    return new Clazz();
}

class myClass {
    public m() { }
}
var instance = myFunction(myClass) // instance is typed as myClass, T is infered to myClass
instance.m() // it works perfectly fine

Typescript has the ability to deduce type parameters based on the arguments provided to a function. Usually, you do not need to explicitly declare type parameters unless absolutely necessary.

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