Disproving Class Validation Problems

[ryasmi]

Class Validation Problems

The following code works as expected in the TS Playground.

class ValidNumber extends Number {
  protected readonly symbol = Symbol()
  constructor(input: unknown) {
    super(input)
    if (typeof input !== 'number' || Number.isNaN(input)) {
      throw new Error('Invalid number')
    }
  }
}

class USD extends ValidNumber {
  protected readonly symbol = Symbol()
  constructor(input: unknown) {
    super(input)
    if (this.valueOf() < 0) {
      throw new Error('Invalid US Dollar amount')
    }
  }
}

class GBP extends ValidNumber {
  protected readonly symbol = Symbol()
  constructor(input: unknown) {
    super(input)
    if (this.valueOf() < 0) {
      throw new Error('Invalid GB Pound amount')
    }
  }
}

export type PlainObject = { [key: string]: unknown }

export function isPlainObject(input: unknown): input is PlainObject {
	return typeof input === 'object' && input !== null && input.constructor === Object
}

class TestObject extends Object {
  public gbp: GBP
  public usd: USD

  constructor(input: unknown) {
    super(input)
    if (!isPlainObject(input)) {
      throw new Error('Invalid object')
    }
    this.gbp = new GBP(input.gbp)
    this.usd = new USD(input.usd)
  }
}

const invalidNum1: USD = 1
const invalidNum2: GBP = 1
const invalidNum3: USD = new GBP(1)
const invalidNum4: GBP = new USD(1)
const invalidNum5: USD = new ValidNumber(1)
const invalidNum6: GBP = new ValidNumber(1)

const validNum1: ValidNumber = new ValidNumber(1)
const validNum2: USD = new USD(1)
const validNum3: GBP = new GBP(1)
const validNum4: ValidNumber = new USD(1)
const validNum5: ValidNumber = new GBP(1)
const validNum6: ValidNumber = new USD(-1) // Will be validated at runtime
const validNum7: ValidNumber = new GBP(-1) // Will be validated at runtime

const invalidObj1: TestObject = { gbp: new USD(1), usd: new GBP(1) }
const invalidObj2: TestObject = { gbp: 1, usd: 1 }

const validObj1: TestObject = { gbp: new GBP(1), usd: new USD(1) }
const validObj2: TestObject = new TestObject({ gbp: new GBP(1), usd: new USD(1) })
const validObj3: TestObject = new TestObject({ }) // Will be validated at runtime