Enten Types

Enten Types is a library to create type-safe guards to check the shape of unknown data

Installation

npm install @i-doit/enten-types

Guards

You can define the shape of the expected data using the type guards.

The following guards are available:

isString, isNumber, isBoolean

These guards check if an argument has a specific type.

For example,

const data = await fetch('/api/data').then(a => a.json());

if (isNumber(data)) {
  // data is a number
}

isObject

isObject checks if an argument is an object.

isObjectWithShape checks if it's an object with predefined shape. It receives key-value pairs with guards for each field.

isMapOf checks if it's an associative array with all values matching the passed guard.

For example,

const isApiEntry = isObjectWithShape({
  id: isString,
  order: isNumber,
  active: isBoolean,
});

const data = await fetch('/api/data').then(a => a.json());

if (isApiEntry(data)) {
  // data has type 
  // {
  //   id: string;
  //   order: number;
  //   active: bool;
  // }
}

if (isMapOf(isApiEntry)(data)) {
  // data has a type Record<string, ApiEntry>
}

isArray

isArray checks if an argument is an array.

isArrayOf checks if an argument is an array and every element of the array matches the passed guard.

For example,

const data = await fetch('/api/data').then(a => a.json());

if (isArrayOf(isApiEntry)(data)) {
  // data has type ApiEntry[]
}

Optional

Optional guard allows you to create a guard that allows undefined.

For example,

const isApiEntry = isObjectWithShape({
  id: isString,
  title: optional(isString),
})

// isApiEntry checks if an argument has the shape:
// {
//   id: string;
//   title?: string; 
// }

isExact

isExact checks if the value has exactly the same value as expected.

This can be useful to create the discriminator maps.

const isEqFilter = isObjectWithShape({
  operation: isExact<'eq'>('eq'),
  value: isString,
  field: isString
});
// EqFilter has type 
// {
//   operation: 'eq';
//   value: string;
//   field: string;
// }

Extracting the type of the Guard

To retrieve the type that supports guard, you can use GetType type:

For example,

const isApiEntry = isObjectWithShape({
  id: isString,
  title: isString,
  name: optional(isString),
});

type ApiEntryType = GetType<typeof isApiEntry>;
// ApiEntryType is 
// {
//    id: string;
//    title: string;
//    name: string | undefined;
// }

This way you can define your type using the guards.

OrX and AndX

You can combine guards together using andX or orX:

const isIdentifiable = isObjectWithShape({
  id: isString
});
const isUser = andX(isIdentifiable, isObjectWithShape({
  username: string
}));

Composition

You can combine your guards to create new ones:

const isApiResponse = isObjectWithShape({
  offset: isNumber,
  total: isNumber,
});
const isUserApiResponse = andX(isApiResponse, isObjectWithShape({
  results: isArrayOf(isUser)
}))

type UserApiResponse = GetType<typeof isUserApiResponse>;

NPM scripts

• npm t: Run test suite
• npm start: Run npm run build in watch mode
• npm run test:watch: Run test suite in interactive watch mode
• npm run test:prod: Run linting and generate coverage
• npm run build: Generate bundles and typings, create docs
• npm run lint: Lints code
• npm run commit: Commit using conventional commit style (husky will tell you to use it if you haven't 😉)