decorator validation

index.ts

function Validate<T extends { new(...args: any[]): {} }>(constructor: T) {
  return class extends constructor {
    errors: string[]

    constructor(...items: any[]) {
      super(...items)
      this.errors = []
      for (const x in this) {
        if (this[x] == undefined) {
          this.errors.push(`property '${x}' was undefined on class '${constructor.name}'`)
        }
      }
    }
  }
}

function validateErrors(obj: any) {
  if (!obj.errors) {
    console.warn("did not find obj metadata")
    return
  }
  if (obj.errors.length) {
    console.error(obj.errors)
  }
}

type ExampleInit = Omit<Example, "doSomething" | "value" | "height">

@Validate
class Example {
  height = 1
  name!: string
  age!: number
  temp?: boolean

  constructor(init: ExampleInit) {
    Object.assign(this, init)
  }

  public get value(): string {
    return "computed value"
  }

  doSomething() {
    console.log("something is called by func")
  }
}

// const e = new Example({ name: 'Graham', age: 12 })
// const e = new Example({ name: 'Graham', age: 12, temp: true })
const e = new Example({ name: 'Graham', age: undefined as any })

// e.doSomething()
console.log("done\n\n\n")
console.log(e)
console.log(e instanceof Example)

validateErrors(e)