如何访问另一个类/ TypeScript 中的类

Question

I have my main class A

export class A {

    public sourceReference: string;

    public charge: Charge;
}

my Charge class looks like such:

export class Charge {

    public chargeType: string;
    
    public chargeAccountNumber: string;

    public chargeCurrency: string;
}

In my index file I want to use my main class A and populate my payload as follows:

    import { A } from "./a";
    
    public static create(payload) {

      let myData = new A();

      myData.sourceReference = payload.sourceRef;
      myData.charge.chargeType = payload.type;
      myData.charge.chargeAccountNumber = payload.accountNumber;
      myData.charge.chargeCurrency = payload.currency

      return JSON.stringify(myData)

     }

my incoming payload file looks like such:

payload = { sourceRef: "1234", type: '615-01', accountNumber: '123456', currency: 'USD'}

I am able to generate myData.sourceReference

However,

The problem is that myData.charge is returning as undefined, resulting in undefined values for myData.charge.chargeType , myData.charge.chargeAccountNumber & myData.charge.chargeCurrency .

Exception: TypeError: Cannot set property 'chargeType' of undefined

Answer 1

Class A has a property of the class Charge .

Having said that, the charge property only has a type - but no instance.

The class A will have to create an instance of the class Charge somewhere - mostly in the constructor.

The constructor should look like this:

export class A {

  public sourceReference: string;
  public charge: Charge;

  constructor() {
     this.charge = new Charge()
  }

 ...

Answer 2

The exception is telling you what's the problem. You have to define myData.charge, using myData.charge = new Charge() and then define it's properties like

myData.charge.chargeType = payload.type;
myData.charge.chargeAccountNumber = payload.accountNumber;
myData.charge.chargeCurrency = payload.currency

Or if you want to be fancy, you can create a constructor for charge like this:

export class Charge {
    
    constructor(chargeType:string, chargeAccountNumber:string, chargeCurrency:string){
    this.chargeType = chargeType;
    this.chargeAccountNumber = chargeAccountNumber;
    this.chargeCurrency=chargeCurrency;
    }

    public chargeType: string;

    public chargeAccountNumber: string;

    public chargeCurrency: string;
}

And then you can call the constructor like

myData.charge = new Charge(chargeType,chargeAccountNumber,chargeCurrency)