Different types of Dependency Injection in JavaScript

di.js

// Dependency Injection

// single dep
const random = Math => Math.random()

random({ random: () => 4 }) // 4
random(Math) // anything between 0 - 1

// multiple deps - as parameters

const report = async (log, saveToDb, Date, message) => {
    log(`{new Date()}: ${message}`)
    await saveToDb(new Date(), message)    
}
// cumbersome...

// multiple deps - destructured
/**
 * @param {object} context
 * @param {object} context.db
 * @param {function} context.log
 */
const readUserFromDbById = async ({ db, log }, id) => {
    const user = await db.where({ id }).fetch()
    log(`user fetched: ${user.name}`)
    return user
}


// multiple deps - object
/**
 * @param {object} context
 * @param {object} context.db
 * @param {function} context.log
 */
const readUserFromDbById = async (context, id) => {
    const user = await context.db.where({ id }).fetch()
    context.log(`user fetched: ${user.name}`)
    return user
}
// other words: ctx (koa style), deps, dependencies, options, settings, opts

const bookshelf = require('bookshelf')

readUserFromDbById({ db: { where: () => ({ fetch: () => ({ name: 'joe' }) }) }, log: () => {} }, 1) // { name: 'joe' }
readUserFromDbById({ db: bookshelf, log: console.log }, 1) 
// user fetched: joe
// { name: 'joe' } or Error or null or { name: null } or ...


// delayed execution
const readUserFromDbById = context => async id => {} // readUserFromDbById(ctx)(3)
const readUserFromDbById = R.curry((context, id) => {}) // readUserFromDbById(ctx)(3) or readUserFromDbById(ctx, 3)

// Alternatively: partial application
const readUserFromDbById = async (context, id) => {} // readUserFromDbById(ctx, 3)
readUserFromDbByIdWithContext = R.partial(readUserFromDbById, context)
readUserFromDbByIdWithContext(3)


// module dependencies: function level 

const list = ctx => async () => ctx.fs.readJSON('apps.json') // [1,2,3]
const get = ctx => async id => (await list(ctx))[id] // 1

get({ fs })(1) // 1
get({ fs: { readJSON: () => [2,3,4] } })(1) // 2



// module dependencies: dependency level

const list = ctx => async () => ctx.fs.readJSON('apps.json') // [1,2,3]
const get = ctx => async id => (await ctx.list(ctx))[id] // 1

get({ list, fs })() // 1
get({ list: () => [2] })(1) // 2


// closure dependency injection

const appsFactory = ctx => {
    const list = () => ctx.fs.readJSON('apps.json')
    const get = async () => (await list())[0]
    return {
        list,
        get,
    }
}

const apps = appsFactory(ctx)
apps.list() // [1,2,3]
// but calling list() directly is not possible anymore