Create a "frozen" date object

frozen-date.js

// Date objects frozen with `Object.freeze()` are still mutable due to the way
// JavaScript stores the internal value. You can create a truly immutable,
// "frozen" date object by wrapping it in a proxy which ignores set* functions.

const noop = () => {}
const dateProxyHandler = {
  get(target, prop, receiver) {
    if (prop === Symbol.toStringTag) return "Date"
    if (typeof prop === "string" && prop.startsWith("set")) return noop

    const value = Reflect.get(target, prop, receiver)
    return typeof value === "function" && prop !== "constructor"
      ? value.bind(target)
      : value
  },
}

function freeze(value) {
  return value instanceof Date
    ? new Proxy(Object.freeze(new Date(Number(value))), dateProxyHandler)
    : Object.freeze(value)
}

const frozenDate = freeze(new Date())

frozenDate.setHours(0) // noop
frozenDate.getHours() // works :)

JSON.stringify(frozenDate) // works :)

const copiedDate = new Date(Number(frozenDate)) // works :)

Object.prototype.toString.call(frozenDate) // "[object Date]"

more.md

More Reading

• https://2ality.com/2014/12/es6-proxies.html
• https://stackoverflow.com/q/34907311/51021