Optimize lodash imports with Rollup.js

There are multiple issues surrounding tree-shaking of lodash. Minifiers, even with dead-code elimination, cannot currently solve this problem. Check out the test showing that even with terser as a minifier, this plugin can still reduce bundle size by 70% for an example input. With this plugin, bundled code output will only include the specific lodash methods your code requires.

There is also an option to use lodash-es for projects which ship CommonJS and ES builds: the ES build will be transformed to import from lodash-es.

This input

import { isNil, isString } from "lodash";
import { padStart as padStartFp } from "lodash/fp";

Becomes this output

import isNil from "lodash/isNil.js";
import isString from "lodash/isString.js";
import padStartFp from "lodash/fp/padStart.js";

useLodashEs for ES Module Output

While lodash-es is not usable from CommonJS modules, some projects use Rollup to create two outputs: one for ES and one for CommonJS.

In this case, you can offer your users the best of both:

Your source input

import { isNil } from "lodash";

CommonJS output

import isNil from "lodash/isNil.js";

ES output (with useLodashEs: true)

import { isNil } from "lodash-es";

Usage

import { optimizeLodashImports } from "@optimize-lodash/rollup-plugin";

export default {
  input: "src/index.js",
  output: {
    dir: "dist",
    format: "cjs",
  },
  plugins: [optimizeLodashImports()],
};

Options

Configuration can be passed to the plugin as an object with the following keys:

exclude

Type: String | Array[...String] Default: null

A minimatch pattern, or array of patterns, which specifies the files in the build the plugin should ignore. By default no files are ignored.

include

Type: String | Array[...String] Default: null

A minimatch pattern, or array of patterns, which specifies the files in the build the plugin should operate on. By default all files are targeted.

useLodashEs

Type: boolean Default: false

If true, the plugin will rewrite lodash imports to use lodash-es.

Note: the build will fail if your Rollup output format is not also set to es, esm, or module!

appendDotJs

Type: boolean Default: true

If true, the plugin will append .js to the end of CommonJS lodash imports.

Set to false if you don't want the .js suffix added (prior to v3.x, this was the default).

Vite Compatibility

This plugin "just works" as a Vite 3.x plugin. Simply add it to plugins in your Vite config:

import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";
import { optimizeLodashImports } from "@optimize-lodash/rollup-plugin";

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [react(), optimizeLodashImports()],
});

Example Vite output for a use of kebabCase:

| No plugin | With plugin | | ------------------------------------------------------------ | ------------------------------------------------------------ | | dist/assets/index.497fb95b.js 212.88 KiB / gzip: 71.58 KiB | dist/assets/index.54b72c40.js 146.31 KiB / gzip: 47.81 KiB |

A ~23 KiB reduction in compressed size!

Limitations

Default imports are not optimized

Unlike babel-plugin-lodash, there is no support for optimizing the lodash default import, such as in this case:

// this import can't be optimized
import _ from "lodash";

export function testX(x) {
  return _.isNil(x);
}

The above code will not be optimized, and the plugin will print a warning. (Note: Vite supresses these warnings at build time unless --debug is added to the build command.)

To avoid this, always import the specific method(s) you need:

// this import will be optimized
import { isNil } from "lodash";

export function testX(x) {
  return isNil(x);
}

Alternatives

babel-plugin-lodash solves the issue for CommonJS outputs and modifies default imports as well. However, it doesn't enable transparent lodash-es use and may not make sense for projects using @rollup/plugin-typescript which don't wish to add a Babel step.

Other alternatives include eslint-plugin-lodash with the import-scope rule enabled. This works for CommonJS outputs, but may require manual effort to stay on top of imports.