mappet

Lightweight, composable mappers for object transformations/normalization.

---

API Docs | Examples

---

Installation (npm)

npm i -S mappet

Use cases

• Fault tolerant object transformations, no more Cannot read property of undefined.
• Normalizing API responses shape and key names e.g. to camelCase or flattening nested payloads
• Preparing nested API request payloads from flat form data
• Filtering object entries e.g. omitting entries with undefined value
• Per field modifications e.g. null to empty string to make React inputs happy

Examples

Basic

Simple value to value transformation

const schema: = {
  firstName: "first_name",
  cardNumber: "card.number",
};
const mapper = mappet(schema);
const source = {
  first_name: "Michal",
  last_name: "Zalecki",
  card: {
    number: "5555-5555-5555-4444",
  },
};
const result = mapper(source);
// {
//   firstName: "Michal",
//   cardNumber: "5555-5555-5555-4444",
// }

Mapping values

Third element of schema entry is modifier which allows for mapping values. Modifier accepts current value and entire, original source object.

const formatDate = (date, source) => moment(date).format(source.country === "us" ? "MM/DD/YY" : "DD/MM/YY");
const upperCase = v => v.toUpperCase();

const schema = {
  country: ["country", upperCase],
  date: ["date", formatDate],
};
const mapper = mappet(schema);
const source = {
  country: "gb",
  date: "2016-07-30",
};
const result = mapper(sourceUS);
// {
//   country: "GB",
//   date: "30/07/16",
// }

Filtering entries

Fourth element of schema entry is filter which allows for omitting entry based on its value or entire, original source object.

const skipIfNotAGift = (value, source) => source.isGift;

const schema = {
  quantity: ["quantity"],
  gift: {
    message: ["giftMessage", undefined, skipIfNotAGift],
    remind_before_renewing: ["remindBeforeRenewingGift", undefined, skipIfNotAGift],
  },
};
const mapper = mappet(schema);
const source = {
  quantity: 3,
  isGift: false,
  giftMessage: "All best!",
  remindBeforeRenewingGift: true,
};
const result = mapper(sourceNotGift);
// {
//   quantity: 3,
// };

Composing mappers

Mappers are just clojures. It's easy to combine them using modifiers.

const userSchema = {
  firstName: "first_name",
  lastName: "last_name",
};
const userMapper = mappet(userSchema);

const usersSchema = {
  totalCount: "total_count",
  users: ["items", users => users.map(userMapper)],
};
const usersMapper = mappet(usersSchema);

const source = {
  total_count: 5,
  items: [
    { first_name: "Michal", last_name: "Zalecki" },
    { first_name: "Foo", last_name: "Bar" },
  ],
};
const result = usersMapper(source);
// {
//   totalCount: 5,
//   users: [
//     { firstName: "Michal", lastName: "Zalecki" },
//     { firstName: "Foo", lastName: "Bar" },
//   ],
// }

Strict mode

Mappers in strict mode will throw exception when value is not found on source object.

const schema: = {
  firstName: "first_name",
  lastName: "last_name",
};
const mapper = mappet(schema, { strictMode: true });
const source = {
  first_name: "Michal",
};
const result = mapper(source);
// Uncaught Mappet: last_name not found

You can specify mapper name for easier debugging.

const userMapper = mappet(schema, { strictMode: true, name: "User Mapper" });
const user = mapper(source);
// Uncaught User Mapper: last_name not found

Greedy mode

Mappers in greedy mode will copy all properties from source object.

const schema = {
  last_name: ["last_name", str => str.toUpperCase()],
};
const mapper = mappet(schema, { greedyMode: true });
const source = {
  first_name: "Michal",
  last_name: "Zalecki",
  email: "example@michalzalecki.com",
};
const actual = mapper(source);
// {
//   first_name: "Michal",
//   last_name: "ZALECKI",
//   email: "example@michalzalecki.com",
// }

See tests for more examples.