Optimization of Lodash styling and bundle size

Lodash is one of the most widely used libraries in modern web development. Whether your webapp is based on Angular, React, Vue or something more exotic – chances that you use Lodash are pretty high. Lodash provides tons of utility methods, making your code more fast and elegant.

However, those tons of useful methods come with a cost – Lodash “weights” more than 70 KB of minified code. This is a significant addition even for the heavy apps. Moreover, chances are you are using just a handful of methods from the whole library. Tree shaking provided by your favorite packing tool could help, but here it comes the next issue – there are several possible ways you can import Lodash in your ES6-based code, potentially making it “unshakable”:

// Method 1:
// import the whole library
import _ from 'lodash';

// Method 2:
// import only relevant methods
import { map, find, filter } from 'lodash';

// Method 3:
// import individual modules
import map from 'lodash/map';
import find from 'lodash/find';
import filter from 'lodash/filter';

Each one of those methods has own pros and cons (and they are described in depth in this excellent article from BlazeMeter), but in many cases personal choice of the developer plays more significant role than formal recommendations. In big projects dealing with the styling of Lodash imports alone may quickly become a mess, and a single “whole library” import will eliminate all your bundle size optimization efforts.

Fortunately, there is a way to handle both size and styling issues together – with the help of Lodash plugins for Eslint and Babel.

Eslint plugin for Lodash enforces consistent and recommended styling for Lodash usage. I’ve found rules coming from plugin:lodash/canonical configuration to be a perfect fit for our React application. This set enforces whole package imports with _ as the name for Lodash variable, enforces usage of Lodash methods over native counterparts when available, and much more. The only caveat I found was in the testing code, where it confused enzyme.find() with native method. Fortunately, we have separate eslint configuration for testing code, so it was pretty easy to tweak the offending rule without sacrificing the style of the application code.

Babel plugin for Lodash implicitly transforms recommended _ imports to per-module imports, reducing “tree-shaked” bundle size. For the app that I was experimenting with, applying both plugins effectively reduced the size of the app bundle by more than 42 KB – but your mileage may vary.

In addition, I spent some time looking at webpack plugin for Lodash, but ultimately decided to skip it. The plugin strips out significant parts of internal Lodash implementation, claiming that those parts are rarely used. While the plugin is configurable, maintaining this configuration will be a pain. Moreover, the code that is unit-tested may be significantly different from the code that is being packaged, especially around edge cases. In my opinion, potential gain in bundle size does not justify the risks of the implementation.

There is one more thing that is worth mentioning in this context. Don’t use Lodash chaining – neither explicit (with _.chain(arr)...) nor implicit (with _(arr)...), since this again will import the whole Lodash library. There are more details about it in this Medium post. In some cases, where chaining seems to be the most simple and elegant way of doing things, see if you can get away with flow and lodash/fp combination:

import { flow, map, compact } from 'lodash/fp';

const result = 
  flow(
    map(...),
    compact
  )(arr);

You can read more about functional programming with Lodash here.

Happy Lodashing!

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