Why is my Singlton constant not staying constant

Question

I am trying to create a singleton module that can store data. I want to be able to edit this date only with setters or public functions and only access it with getters.

I was able to create a getter, setter and a set function. However, I ran into a problem I cant explain when I tried to create a reset function.

I store my default settings in const _defPorts.

I then assign let _myPorts = _defPorts. (I want to create a private variable _myPorts that is initialised with the constant values from _defPorts.

The problem is when I start setting new values, which I expect will only alter _myPorts, it seems to also change my _defPorts values. I don't understand what I am doing wrong or how it is possible that my const value is being changed. Because of this the reset function does not work.

In my console.log I am only displaying the value of _defPorts to show at which point it changes value.

I feel my problem is with the setPorts function but I do not know how to fix it. Any help or advice would be greatly appreciated! :)

This is the Singleton Module I am trying to create:

'use strict'
let activeConfig = (function () {
  const _defPorts = {
    http: 80,
    https: 443,
    secure: false
  }

  let _myPorts = _defPorts

  let setPorts = function (value) {
    console.log('SP->', _defPorts)
    if (value) {
      Object.keys(value).forEach((key) => {
        if (typeof _myPorts[key] !== 'undefined') {
          _myPorts[key] = value[key]
        }
      })
    }
  }

  return {
    setPorts: setPorts,
    resetConfig: function () {
      console.log('RC->', _defPorts)
      _myPorts = _defPorts
    },
    get instance() {
      console.log('GI->', _defPorts)
      return this
    },
    get ports() {
      console.log('GP->', _defPorts)
      return _myPorts
    },
    set ports(value) {
      return setPorts(value)
    }
  }
})()
module.exports = activeConfig

This is the code I am testing it with:

'use strict'
const {
  ports,
  instance: activeConfig
} = require('./activeConfig/activeConfig')

console.log('1 ->', activeConfig)
console.log('2 ->', activeConfig.ports)

activeConfig
  .setPorts({
    secure: true,
    http: 8080
  })

console.log('3 ->', ports)

activeConfig.ports = {
  secure: true,
  https: 4444
}

console.log('4 ->', ports)
console.log('RESET')
activeConfig.resetConfig()
console.log('5 ->', activeConfig.ports)

This is the console log output:

GP-> { http: 80, https: 443, secure: false }
GI-> { http: 80, https: 443, secure: false }
1 -> {
  setPorts: [Function: setPorts],
  resetConfig: [Function: resetConfig],
  instance: [Getter],
  ports: [Getter/Setter]
}
GP-> { http: 80, https: 443, secure: false }
2 -> { http: 80, https: 443, secure: false }
SP-> { http: 80, https: 443, secure: false }
3 -> { http: 8080, https: 443, secure: true }
SP-> { http: 8080, https: 443, secure: true }
4 -> { http: 8080, https: 4444, secure: true }
RESET
RC-> { http: 8080, https: 4444, secure: true }
GP-> { http: 8080, https: 4444, secure: true }
5 -> { http: 8080, https: 4444, secure: true }