keyMirror with namespaces

README.md

var data = keyMirror({
  ONE: null,
  TWO: null,
  
  OTHER: keyMirror({
    STUFF: null
  }, "OTHER")
});

yields

var data = {
  ONE: "ONE",
  TWO: "TWO",
  
  OTHER: {
    STUFF: "OTHER:STUFF"
  }
};

keyMirror.js

/**
 * Given an object of `key -> null` pairs, returns an object of
 * `key -> key` pairs. Leaves `key -> other` pairs untouched.
 * An optional second parameter prefixes the values, e.g.
 * a second parameter of "NAMESPACE" returns
 * `key -> "NAMESPACE:" + key` pairs
 */
function keyMirror(obj, namespace) {
  var ret = {},
      prefix = namespace ? namespace + ":" : "",
      key;

  for (key in obj) {
    if (!obj.hasOwnProperty(key)) {
      continue;
    }

    if (obj[key] === null) {
      ret[key] = prefix + key;
    } else {
      ret[key] = obj[key];
    }
  }

  return ret;
};