concatenative inheritance two methods with same signature

The code below prints only the event contents, how do I make that print WheatherData.value number? I am coming from java and I am used to do it this way.

const Event = (time, place) => {
    var _time = time
    var _place = place

    return {
        getTime() {
            return _time
        },
        getPlace() {
            return _place
        },
        updateTime() {
            _time = new Date(Date.now())
        },
        toString() {
            return 'Time: ' + _time + 'nPlace: ' + _place
        }
    }
}

const WeatherData = (value, time, place) => {
    var _event = Event(time, place)
    var _value = value
    const getValue = () => { return _value }
    const toString = () => { return 'nValue: ' + _value + _event.toString() }
    return Object.assign({ getValue, toString }, _event)
}



const wd = WeatherData(10.1, new Date(Date.now()), 'Chisinau, Moldova')

console.log(wd.toString())

//Time: Sat Sep 18 2021 08:49:10 GMT+0200 (Central European Summer Time)
//Place: Chisinau, Moldova
// no value printed

Answer

return Object.assign({ getValue, toString }, _event)

The line above causing the problem. When you assign _event object to { getValue, toString } object you are simply overriding toString method of WeatherData function. Instead, just return { getValue, toString } from your WeatherData function, like below;

const WeatherData = (value, time, place) => {
    var _event = Event(time, place);
    var _value = value

    const getValue = () => { return _value }
    const toString = () => { return 'nValue: ' + _value + 'n' + _event.toString() }

    return { getValue, toString }
}