Object.getRealmOf.js

Object.getRealmOf.js

#!/usr/bin/env node

"use strict"
//const global = (typeof(global) != "undefined") ? global : this

//# or { null } if you dont want cache
let cache = new WeakMap()

const isPrimitive = (v) => {
  return v !== Object(v)
}

 ;(global.Reflect || {  }).getRealmOf = Object.getRealmOf = function(obj) {
  if(isPrimitive(obj)) {
    return null
  }
  else {
    const objProto = Object.getPrototypeOf(obj)
    if(objProto == null) {
      return null
    }
    else {
      const RealmFunction = (objProto
        .constructor // Class
        .constructor // Function
      )

      if(RealmFunction == Function) {
        return global
      }
      else {
        const getAndCache = function(get) {
          if(cache != null) {
            let tmp = null
            return cache.get(RealmFunction) || (tmp = get(), cache.set(RealmFunction, tmp), tmp)
          }
          else {
            return get()
          }
        }

        return getAndCache(() => RealmFunction("return this")())
      }
    }
  }
}

const example = (f) => {
  try {
    f()
  }
  catch(err) {
    console.log(`Test failded, err = #{ err }`)
    throw err
  }
  console.log("Test passed")
}

const assert = function(expr, msg) {
  if(!expr) {
    throw msg || ""
  }
  else {
    
  }
}

example(() => {
  assert(Object.getRealmOf("") == null)
  assert(Object.getRealmOf(Object.create(null)) == null)
  assert(Object.getRealmOf([]) == global)

  let createRealm = null
  if(global.require != null && global.require("vm") != null) {
    const vm = require("vm")
    createRealm = function() {
      const sandbox = {  }
      vm.createContext(sandbox)
      return {
        sandbox,
        eval(code) {
          vm.runInContext(code, sandbox)
        }
      }
    }
  }
  else {

  }

  if(createRealm != null) {
    let realm = createRealm()
    assert(Object.getRealmOf(realm.eval("[]")) == realm.eval("this"))
  }
  else {

  }

})

//# typical usecases
example(function() {
  let obj = []
  assert(obj instanceof Object.getRealmOf(obj).Array)
  assert(obj instanceof Object.getRealmOf(obj).Object)
})