mappet
Lightweight, composable mappers for object transformations/normalization.
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
undefinedvalue - Per field modifications e.g.
nullto 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
Schema entries can be also option objects of path, modifier, and include. Modifier accepts selected value and 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: { path: "country", modifier: upperCase },
date: { path: "date", modifier: formatDate },
};
const mapper = mappet(schema);
const source = {
country: "gb",
date: "2016-07-30",
};
const result = mapper(source);
// {
// country: "GB",
// date: "30/07/16",
// }Filtering entries
Using include you can control which values should be keept and what dropped.
const isGift = (value, source) => source.isGift;
const schema = {
quantity: ["quantity"],
message: { path: "giftMessage", include: isGift },
remind_before_renewing: { path: "remindBeforeRenewingGift", include: isGift },
};
const mapper = mappet(schema);
const source = {
quantity: 3,
isGift: false,
giftMessage: "All best!",
remindBeforeRenewingGift: true,
};
const result = mapper(source);
// {
// quantity: 3,
// };Composing mappers
Mappers are just closures. 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: { path: "items", modifier: users => users.map(userMapper) },
};
const usersMapper = mappet(usersSchema);
const source = {
total_count: 5,
items: [
{ first_name: "Michal", last_name: "Zalecki" },
{ first_name: "John", last_name: "Doe" },
],
};
const result = usersMapper(source);
// {
// totalCount: 5,
// users: [
// { firstName: "Michal", lastName: "Zalecki" },
// { firstName: "John", lastName: "Doe" },
// ],
// }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, { strict: true });
const source = {
first_name: "Michal",
};
const result = mapper(source);
// Uncaught Mappet: last_name not foundYou 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 foundGreedy mode
Mappers in greedy mode will copy all properties from source object.
const schema = {
last_name: { path: "last_name", modifier: str => str.toUpperCase() },
};
const mapper = mappet(schema, { greedy: 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.
