How to replace class properties with another class' properties dynamically in TypeScript-CodePudding

I have the following TypeScript code that attempts to replace the values of the properties of one class instance with the values of another using a loop.

class A {

    n: number = 1
    s: string = "hello"

}

const myA1 = new A()
const myA2 = new A()
myA2.n = 2
myA2.s = "hi"

for (const k of Object.keys(myA1)) {
    /* Type 'string | number' is not assignable to type 'never'.
    Type 'string' is not assignable to type 'never'. */
    myA1[k as keyof A] = myA2[k as keyof A]
}

I know I could manually replace the properties like so:

myA1.n = myA2.n
myA1.s = myA2.s

However, I would like to replace them dynamically. Is there a way to tell TypeScript that I know the properties are of the same type? because they are (the same keys are being used for instances of the same class).

A follow-up question I also have is: what if the classes were different, but I also knew that their properties with the same name have the same type? Could the value replacement also be done in typescript?

I welcome any solutions or proposals following the same or another line of thought and logic. Avoiding things like type assertions would be fantastic.

Thank you

CodePudding user response：

You can do this via generics. Although, a cast is required for Object.entries(a) because TS isn't smart enough to know it is (keyof typeof a)[] which is just (keyof T)[]. Here's your solution:

class A {
    n: number = 1
    s: string = "hello"
}

const myA1 = new A()
const myA2 = new A()

function copyProps<T>(a: T, b: T) {
    for (const k of Object.keys(a) as (keyof T)[]) {
        a[k] = b[k];
    }
}

copyProps(myA1, myA2);

TypeScript Playground Link

CodePudding user response：

It is possible to use Object.assign() method:

The Object.assign() method copies all enumerable own properties from one or more source objects to a target object. It returns the modified target object.

An example:

class A {

    n: number = 1
    s: string = "hello"

}

const myA1 = new A()
const myA2 = new A()


myA1.n = 1;
myA2.n = 2;
myA1.s = "s1"
myA2.s = "s2"

const assigned = Object.assign(myA1, myA2)
console.log(`assigned`, assigned)
console.log(`myA1`, myA1)
console.log(`myA2`, myA2)

Or you can use spread syntax:

class A {
    n: number = 1
    s: string = "hello"
}

const myA1 = new A()
const myA2 = new A()


myA1.n = 1;
myA2.n = 2;
myA1.s = "s1"
myA2.s = "s2"

const assigned = {...myA1, ...myA2};
console.log(`assigned`, assigned)
console.log(`myA1`, myA1)
console.log(`myA2`, myA2)