mappet
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Lightweight, composable mappers for object transformations
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# mappet
[](https://circleci.com/gh/MichalZalecki/mappet)
Lightweight, composable mappers for object transformations/normalization.
***
[API Docs](https://michalzalecki.github.io/mappet) | [Examples](#examples)
***
## Installation ([npm](https://www.npmjs.com/package/mappet))
```
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
```js
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.
```js
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.
```js
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.
```js
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.
```js
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 found
```
You can specify mapper name for easier debugging.
```js
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.
```js
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](src/mappet.spec.ts) for more examples.