TypeScript：带有构造函数的类，该构造函数根据传入的参数调用方法

Question

I have a regular TS class looking like this:

export class Company {
  private firmId: number;
  private regNr: string;
  private firmName: string;
  private address: string;
  private status: string;
  private town: string;
  private zip: string;
  private postAddress: string;
  private tel1: string;
  private tel2: string;
  private fax: string;
  private eMail: string;
  private homepage: string;
  private webshow: string;
  private bankcode: string;
  private bankaccount: string;
  private contact: string;
  private addidata: string;
  private entryDate: string;
  private userId: string;
  private infoEMail: string;
  private pfId: string;
  private pfName: string;
  private country: string;

  constructor(company: any) {
    this.firmId = company.firmId;
    this.regNr = company.regNr;
    this.firmName = company.firmName;
    this.address = company.address;
    this.status = company.status;
    this.town = company.town;
    this.zip = company.zip;
    this.postAddress = company.postAddress;
    this.tel1 = company.tel1;
    this.tel2 = company.tel2;
    this.fax = company.fax;
    this.eMail = company.eMail;
    this.homepage = company.homepage;
    this.webshow = company.webshow;
    this.bankcode = company.bankcode;
    this.bankaccount = company.bankaccount;
    this.contact = company.contact;
    this.addidata = company.addidata;
    this.entryDate = company.entryDate;
    this.userId = company.userId;
    this.infoEMail = company.infoEMail;
    this.pfId = company.pfId;
    this.pfName = company.pfName;
    this.country = company.country;
  }
}

This constructor is obviously very fat and I am considering refactoring to builder pattern, but for now it is like this.

This class is instantiated with a JSON response, that has absolutely the same field structure.

The problem arises when I need to instantiate this class with empty values in order for Angular form validation to work correctly.

How can I achieve that? Can I create a constructor which calls the methods of this class depending upon the constructor parameters, something like this:

export class Company {
  // list of fields ...
  constructor(company: any) {
    if (company != '') {
      this.instantiateEmpty();
    } else {
      this.instantiateWithData();
    }
  }

  private instantiateEmpty() {
    // create empty fields of class
  }

  private instantiateWithData() {
    // create filled fields
  }
}

Or should I create this class with a builder-like approach and just use correct static method depending upon what I need to do with the class: instantiate with data or instantiate with empty fields?

Thanks!

Answer 1

Let's start with Object.assign which will make your constructor very slim:

constructor(company: any) {
    Object.assign(this, company);
}

It will work only if, as you wrote, the company object has the same fields as the class.

Now, you can also have a different signature to your constructor:

constructor();
constructor(company: any);
constructor(company?: any) {
    if (comapny) {
        Object.assign(this, company);
    } else {
        ....
    }
}

---

Edit

In order to initialize all the fields with empty values, I recommend having a constant object which has the same exact fields as the class but with empty fields, then use Object.assign with it, something like:

const DEFAULT_VALUES = {
    firmId: 0,
    regNr: "",
    ...
}

class Company {
    constructor();
    constructor(company: any);
    constructor(company?: any) {
        if (comapny) {
            Object.assign(this, company);
        } else {
            Object.assign(this, DEFAULT_VALUES);
        }
    }
}

Or even just:

class Company {
    constructor(company: any = DEFAULT_VALUES) {
        Object.assign(this, company);
    }
}

Answer 2

EDIT: As pointed out in the comments below - due to the way TS behaves - this solution will not copy over methods of a class to the object. So it's not really the recommended path to use.

---

There is no need to use a constructor class here.

Without a constructor, if you have a JSON which reflects the company structure you want you can simply cast the JSON into the object like so:

let company: Company = jsonThatIsACompany;

If you don't have a JSON object to cast, and need an empty object, simply make a new instance of the class:

let company: Company = new Company()

This will be an instance of the object with all empty fields.

With this in mind you do not need a constructor function in your class. You can just declare the properties as normal.

eg:

export class Company {
  firmId: number;
  regNr: string;
  firmName: string;
  address: string;
  status: string;
  town: string;
  zip: string;
  postAddress: string;
  tel1: string;
  tel2: string;
  fax: string;
  eMail: string;
  homepage: string;
  webshow: string;
  bankcode: string;
  bankaccount: string;
  contact: string;
  addidata: string;
  entryDate: string;
  userId: string;
  infoEMail: string;
  pfId: string;
  pfName: string;
  country: string;
}

The only big difference is you'll need to stop using private on the properties so they can be accessed and changed by whatever is using the object (useful for forms).

Answer 3

As an aside if you were not wanting to use the JSON to populate, you domnt need to define/assign all those properties manually - you can use constructor parameters to do it automatically for you to keep it DRY...

export class Company {

  // declaring constructor parameters with access level 
  // auto defines the class properties for you...
  constructor(private firmId: number,
              private regNr: string,
              private firmName: string,
              private address: string,
              private status: string,
              private town: string,
              private zip: string,
              private postAddress: string,
              private tel1: string,
              private tel2: string,
              private fax: string,
              private eMail: string,
              private homepage: string,
              private webshow: string,
              private bankcode: string,
              private bankaccount: string,
              private contact: string,
              private addidata: string,
              private entryDate: string,
              private userId: string,
              private infoEMail: string,
              private pfId: string,
              private pfName: string,
              private country: string) {
    // also no need to assign them in here...they are automatically assigned
  }

}