Javascript - 将类实例保存到哈希表/对象中并使用关键实例函数

Question

I have 2 classes Key and Session that output unique "this.session/this.key" values on every class instance:

//self executing function or IIFE(Immediately Invoked Function Expression) 
//classes that return unique key and sessions on every instance

const Session = (() => {
    let lastSession = 80
    return class Session{
        constructor(){
            this.session = lastSession
            lastSession++
        }

        printSession(){
            console.log(this.session)
        }
    }
})()

const Key = (() => {
    let lastKey = 0

    return class Key{
        constructor(){
            this.key = lastKey
            lastKey++
        }

        printKey(){
            console.log(this.key)
        }
    }
})()

I have a third class Manager that adds {Key:Session} instance pairs to a Object/Hashtable:

class Manager{
    constructor(){
        this.allSessions = {}
    }

    addSession(){
        this.allSessions[new Key] = new Session
    }

    printSessions(){
        for(let key in this.allSessions){
            console.log(`${key} : ${this.allSessions[key]}`)
            //key.printSession()
            //console.log(key.key)
            //this.allSessions[key].printSession()

        }
    }

}

There are 2 problems:

1)The hashtable/object only has 1 {Key:Session} pair at any given time. No matter how many addSession() calls I make. Is this because it treats all the Key instances as the same? How do I fix this.

2)In the printSessions() function within Manager class, I can't seem to print out the key using key.printKey() that I defined in the key class? Why is that? I also tried console.log(key.key) which also did not work.

Answer 1

You're trying to use instances of the Key class as object property names. That doesn't work; property names are always strings, so the objects (the Key objects) are converted to strings implicitly. That always results in the string "[object Object]".

You can instead try

    this.allSessions[new Key().key] = new Session

Plain JavaScript objects indeed seem like hash tables, but the keys can only be strings. You might want to explore the Map type.

Answer 2

The fact that you call the instance key and that instance also has a property called key is maybe the reason you made this error.

Also, printing this.allSessions[key] is not really helpful as that is an object. Maybe you intended: this.allSessions[key].session :

class Manager{
    constructor(){
        this.allSessions = {}
    }

    addSession(){
        this.allSessions[(new Key).key] = new Session
    }

    printSessions(){
        for(let key in this.allSessions){
            console.log(`${key} : ${this.allSessions[key].session}`)
        }
    }
}