Implement.js

• Create interfaces to enforce, remove, or rename properties of objects
• Use in testing to easily verify object shapes and property types
• Effortlessly and safely parse API responses by renaming or removing properties
• Errors and warnings are suppressed when process.env.NODE_ENV === 'production'

Docs

• What is Implement.js
• Setup
• API
  • implements
  • Interface
  • type
  • ES6 Modules / CommonJS
• Examples
  • Standard usage
  • Renaming and refactoring API responses

What is Implement.js?

Implement.js is a library that attempts to bring interfaces to JavaScript in the form of runtime type-checking.

Simply define an interface using Interface and call implement on an object to check if it implements the given interface.

const Hello = {
    greeting: 'hello'
    wave () {}
}
const Introduction = Interface('Introduction')({
    greeting: type('string')
    handshake: type('function')
}, { error: true })
 
const HelloIntroduction = implement(Introduction)(Hello) // throws an error!

Setup

Install

yarn add implement-js

Build

yarn build

API

Implement

Accepts an Interface and an object, then checks to see if the object implements the given Interface.

implement(Interface)(object) -> object

Implementing classes

Since class is just a constructor function waiting to be called and not truly an object, we cannot check if it implements a given Interface. Also, due to the dynamic nature of class properties, even once instantiated we cannot reliably implement interfaces against them.

Interface

Takes a string to be used as a name, if none is provided it generates a uuid, returns a function that accepts an object where all the keys are type objects, and returns an Interface. The Interface is to be used by implement.

Interface([name])(object[, options]) -> Interface object

Options

{
    // when true, errors and warnings are triggered when properties
    // other than those on the Interface are found, is suppressed if
    // trim is set to true - default: false
    strict: true,
 
    // remove methods that don’t match the Interface - default: false
    trim: true,
 
    // throws an error when Interface isn’t implemented - default: false
    error: true,
 
    // warns when Interface isn’t implemented - default: true
    warn: false,
 
    // accepts an Interface to extend, the new Interface must also
    // implement the extended Interface
    extend: Interface,
 
    // accepts an object where all property values are strings used to
    // rename the corresponding properties on the given object
    rename: { seats: 'chairs' }
}

Type

Accepts a string matching any JavaScript types, plus ‘array’ and 'any'.

If ‘array’ is passed, a second argument can be passed denoting the type of the elements of the array, if none is passed then the types of the elements will not be checked. The second argument should be an array containing type objects.

If ‘object’ is passed, a second argument can be passed containing an Interface for the object, if none is passed then the properties of the object will not be checked. The second argument should be an Interface.

type(string[, Array<type>|Interface]) -> Type

ES6 Modules / CommonJS

// ES6
import implement, { Interface, type } from 'implement-js'
 
// CommonJS modules
const implementjs = require('implement-js')
const implement = implementjs.default
const { Interface, type } = implementjs

Examples

Standard usage

import implement, { Interface, type } from 'implement-js'
 
const Passenger = Interface('Passenger')({
    name: type(‘string’),
    height: type(‘number’)
})
 
const ChildPassenger = Interface('ChildPassenger')({
    hasBabySeat: type(‘boolean’)
}, {
    extend: Passenger
})
 
const Car = Interface('Car')({
    speed: type(’number’),
    passengers: type(‘array’, [type('object', Passenger), type('object', ChildPassenger)]),
    beep: type(‘function’)
}, { error: true })
 
// Successful implementation
const MyCar = implement(Car)({
    speed: 0,
    passengers: [],
    beep () {}
})
 
// Bad implementation - does not implement the beep method
const AnotherCar = implement(Car)({
    speed: 0,
    passengers: []
})

Unit tests

import implement from 'implement-js'
import CarService from '../services/CarService'
import { Vehicle } from '../Interfaces'
 
describe('CarService', () => {
    describe('getCar', () => {
        it('should implement the Vehicle Interface', done => {
            const someCar = CarService.getCar()
 
            // Ensure someCar implements Vehicle Interface
            implement(Vehicle)(someCar)
 
            done()
        })
    })
})

Renaming and refactoring API responses:

import { store } from ‘../store’
import { fetchUsers } from ‘../services/userService’
import implement, { Interface, type } from 'implement-js'
 
const User = Interface('User')({
    name: type(‘string’),
    id: type(‘number’)
}, { trim: true })
 
const Users = Interface('Users')({
    users: type(‘array’, [type('object', User)])
}, {
    trim: true,
    rename: { API_RESPONSE_USERS_LIST: 'users' }
})
 
const updateUsers = () => async dispatch => {
    dispatch(fetchUsersBegin())
 
    try {
        const users = await fetchUsers()
        const MyUsers = implement(Users)(users)
 
        dispatch(updateUsersSuccess(MyUsers))
    } catch (err) {
        dispatch(updateUsersError(err))
    }
}

Code Style

eslint-config-standard