lodash.chain

If you're a JavaScript developer in 2017, you've probably already heard of lodash. If not though, it's a collection of 300-ish utility functions that exist to fill gaps in JavaScript's relatively small standard library. lodash is one of the most popular packages in the npm registry, and is depended on by over 25,000 other modules in the registry.

JavaScript's Arrayobject has some really useful methods for working with collections of data, like forEach, map, reduce, every, and filter. These methods are often good enough, but chaincan make working with collections even sweeter.

Let's take a contrived example. Say you have an array of user objects, and you want to get the email addresses of all active users, sorted by the date they signed up. Let's also say that some users don't have email addresses, so you want to filter those out.

Using vanilla JavaScript:

users
  .filter(user => user.active === true)
  .sort((a, b) => a.signupDate.localeCompare(b.signupDate))
  .map(user => user.email)
  .filter(names => name && name.length)

Using chain:

const {chain} = require('lodash')

chain(users)
  .filter('active')
  .orderBy('signupDate')
  .map('email')
  .compact()
  .value()

I find that second version is easier to write, and easier to read.

Note the value() call at the end. Remember to always call that last.

A chain object works just like a JavaScript array, but with all of lodash's convenience methods attached to its prototype. A few of my favorites:

• first returns the first element in the collection
• last returns the last
• flatten turns arrays of arrays into one flat array
• compact removes falsy values
• pick lets you specify which properties you want from each object
• omit lets you specify which properties you don't want from each object
• orderBy sorts by a property name and optional direction asc or desc
• sample returns a random element
• shuffle randomly arranges the values

There are lots of them. See lodash.com/docs.

Life after Ruby

For many years I was a rubyist. That is, a reader and writer of the Ruby programming language. I loved the expressiveness and flexibility of Ruby, and in particular I loved its Enumerablemodule which, like chain, provides a bunch of really useful methods for working with collections.

When Node.js came along I could tell it was going to be a big deal, but I loved Ruby's syntax and really didn't want to let it go. I would have preferred to continue writing in Ruby forever, but I couldn't ignore the significance of Node.js and the huge effect it was having on JavaScript's growth beyond the browser and into new environments like servers and terminals and IOT devices and robots.

lodash's chain method makes me miss Ruby just a little less. Combined with JavaScript's newish arrow function syntax, I feel like the language is really starting to grow up.

Nota Bene

Nota Bene means "observe carefully" or "take note". I just learned that.

If you're writing code targeting browsers (as opposed to Node) you might want to think twice about using chain, because it will make your bundle bigger. lodash publishes standalone packages to npm like lodash.pick andlodash.uniq, but not chain because it requires all of lodash.

There are a number of ways to roll your own lodash build, though. See the lodash functional programming guide for details.