Iterable safe plain JavaScript object as map.

object-map.js

function objectMap () {
  return Object.defineProperty(Object.create(null), Symbol.iterator, {
    configurable: true, // This descriptor is inspired by Map.prototype[Symbol.iterator]
    writable: true,
    value: function* () {
      for (const key in this) {
        yield [key, this[key]]
      }
    }
  })
}

usage.js

const map = objectMap()

map.foo = 1
map.bar = 2

console.log(map.toString) // undefined
console.log({}.toString)  // ƒ toString() { [native code] }

console.log('foo' in map) // true

console.log(map['bar']) // 2

// Akin to PHP's foreach ($map as $k => $v)
for (const [k, v] of map)
  console.log(k, v) // foo 1
                    // bar 2