如何创建 Typescript 装饰器，根据以“_”开头的属性名称将所有 class 属性设置为不可枚举？

Question

How do you get a Typescript class decorator to call a method that sets any property or method starting with an "_" as non-enumerable property (essentially making it private for serialization purposes)?

Imagine there's a class that's a base class which every other class in my application will extend from:

class Base {
     constructor(data: any){
        Object.assign(this, data)
     }

     _setNonEnumerableProperties(){
        Object.keys(this).forEach(key => {
            if(key[0] === '_')
                Object.defineProperty(this, key, { enumerable: false })
        })
     }
}

And then I have a User class like this:

@nonEnumerablePrivateMembers
class User extends Base {
     public name: string
     public email: string
     private _active: boolean
}

And I create and JSON stringify a User instance like this:

const user = new User({name: 'John', email: 'john@example.com', _active: false})
const jsonUser = JSON.stringify(user)
console.log(jsonUser)

I expect the output to be this:

{ "name": "John", "email": "john@example.com" }

and not this:

{ "name": "John", "email": "john@example.com", "_active": false }

Note that it doesn't include the _active property.

I need to know how to write nonEnumerablePrivateMembers decorator that would call the _setNonEnumerableProperties method on the Base class upon a new instance of the extended class.

Any suggestions?

Answer 1

Overriding the constructor appears to work as intended:

interface Class<T> {
  new(...args: any[]): T
}

function nonEnumerablePrivateMembers<T extends Class<Base>>(cls: T): T {
  return class extends cls {
    constructor(...args: any[]) {
      super(...args);
      this._setNonEnumerableProperties();
    }
  }
}

Playground

Answer 2

I'm sure someone with better TypeScript skills can modify this to be a bit cleaner, but based on the TypeScript decorator docs you can have something like this:

function fixEnumerables<T extends { new (...args: any[]): {} }>(
  constructor: T
) {
  return class extends constructor {
    constructor(...data: any[]) {
      super(data);
      Object.assign(this, data[0]);
      Object.keys(this).forEach(key => {
        if (key[0] === "_") {
          console.log(`Freezing "${key}"`);
          Object.defineProperty(this, key, { enumerable: false });
        }
      });
    }
  };
}

@fixEnumerables
class User {
  public name: string;
  public email: string;
  private _active: boolean;
  constructor(data: any) {}
}

const x = new User({ name: "Sam", email: "email@example.com", _active: false });
console.log(JSON.stringify(x));

// Output
// Freezing "_active"
// {"name":"Sam", "email": "email@example.com"}

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