KV: key-value iteration functions for JavaScript

kv.js

// KV.js
// Hash iteration functions

// Set a value on an object at field, returning object.
function set(object, key, value) {
  // Set value on object at key.
  object[key] = value;
  // Return object.
  return object;
}
exports.set = set;

// Similar to Array.reduce, but for objects.
function reducekv(object, next, reduction) {
  var keys = Object.keys(object);

  for (var i = 0; i < keys.length; i++)
    reduction = next(reduction, keys[i], object[keys[i]]);

  return reduction;
}
exports.reducekv = reducekv;

// Similar to Array.filter, but for objects.
// Takes an object and a predicate function. Predicate is called with
// `key` and `value` for each property on object.
// Returns a new object containing keys and values that pass the predicate test.
function filterkv(object, predicate) {
  return reducekv(object, function (out, key, value) {
    return predicate(key, value) ? set(out, key, value) : out;
  }, {});
}
exports.filterkv = filterkv;

// Similar to Array.reject, but for objects.
// Takes an object and a predicate function. Predicate is called with
// `key` and `value` for each property on object.
// Returns a new object containing keys and values that fail the predicate test.
function rejectkv(object, predicate) {
  return reducekv(object, function (out, key, value) {
    return !predicate(key, value) ? set(out, key, value) : out;
  }, {});
}
exports.rejectkv = rejectkv;

// Similar to `Array.map`, but for objects.
// Takes an object and a mapping function. Maps each `value` in object, setting
// new value at `key` on a new object.
// Returns a new object of mapped values.
function mapv(object, a2b) {
  return reducekv(object, function (out, key, value) {
    return set(out, key, a2b(value));
  }, {});
}
exports.mapv = mapv;

// Basic extend function.
function extend(a, b) {
  return reducekv(b, set, a);
}
exports.extend = extend;