little-store

Super simple curried storage in a given plain object when you just must have mutable state

Install and use

npm install --save little-store

const littleStore = require('little-store')
const o = {}
const setFoo = littleStore(o, 'foo')
setFoo(o, 42) // returns 42
// o is {foo: 42}

Why?

Mostly this is a convenient curried function for storing side data in promise chains. With most functions only taking and passing a single argument, storing intermediate values is a pain (see my blog post). Functional libraries like Ramda and Lodash have nice utilities for getting a property from a given object, like _.property, but I could not find a simple set property function. Ramda has lenses, but those return a new object (which is nice) and this is not what I needed. Thus I was forced to do something like this - make a closure just to keep data from the first call

function login () {
    return getUsername()
        .then(function (username) {
            return getPassword()
                .then(function (password) {
                    // check username and password
                })
        })
}

We can store the intermediate results from each promise in local mutable object

function login () {
    const state = {}
    return getUsername()
        .then((s) => {state.username = s})
        .then(getPassword)
        .then((s) => {state.password = s})
        .then(function () {
            // check username and password from state
        })
}

A lot more steps but smaller pyramid of promise doom.

With generators, this is a lot less code, but not as simple to start in most cases

function * checkPassword () {
    const username = yield getUsername()
    const password = yield getPassword()
    // check username and password
}

With little-store creating little "set" callbacks is simple (even multiple ones)

const store = require('little-store')
function login () {
    const state = {}
    return getUsername()
        .then(store(state, 'username'))
        .then(getPassword)
        .then(store(state, 'password'))
        .then(function () {
            // check username and password from state
        })
}

We can even avoid store(state, ...) boilerplate since the littleStore is curried

const store = require('little-store')
function login () {
    const state = {}
    const remember = store(state)
    return getUsername()
        .then(remember('username'))
        .then(getPassword)
        .then(remember('password'))
        .then(function () {
            // check username and password from state
        })
}

Related

• functional-pipeline is a utility for convenient data access and method calls.

Small print

Author: Gleb Bahmutov <[email protected]> © 2016

• @bahmutov
• glebbahmutov.com
• blog

License: MIT - do anything with the code, but don't blame me if it does not work.

Support: if you find any problems with this module, email / tweet / open issue on Github

MIT License

Copyright (c) 2016 Gleb Bahmutov <[email protected]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.