class C {
    constructor() {
        this.constructorOnly = 0
        this.constructorUnknown = undefined
    }
    method() {
        this.constructorOnly = false // error, constructorOnly is a number
        this.constructorUnknown = "plunkbat" //ok,constructorUnknown is string|undefined
        this.methodOnly = 'ok'  // ok, but y could also be undefined
    }
    method2() {
        this.methodOnly = true  // also, ok, y's type is string | boolean | undefined
    }
}