Object to Map, recursive-style

toMap.js

const toMap = (() => {
  const convert = (obj, map = new Map(), keys = Object.keys(obj).values()) => {
    const state = keys.next();
    if (state.done) return map;
    const key = state.value;
    map.set(key, obj[key]);
    return convert(obj, map, keys);
  };
  return obj => obj instanceof Map ? obj : convert(obj);
})();

Example:

toMap({ foo: 1, bar: 2 }); // => Map { foo: 1, bar: 2 }

const toMap = (() => {
  const convert = (obj, map = new Map(), keys = Object.keys(obj).entries()) => {
    const state = keys.next();
    if (state.done) return map;
    const key = state.value[1];
    map.set(key, obj[key]);
    return convert(obj, map, keys);
  };
  return obj => obj instanceof Map ? obj : convert(obj);
})();

works in Firefox :)

Another possibility in Firefox:

const toMap = (() => {
  const convert = (obj, map = new Map(), keys = Object.keys(obj)[Symbol.iterator]()) => {
    const state = keys.next();
    if (state.done) return map;
    const key = state.value;
    map.set(key, obj[key]);
    return convert(obj, map, keys);
  };
  return obj => obj instanceof Map ? obj : convert(obj);
})();

Symbol.iterator is the same as values.