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 this plugin can reduce bundle size by 70% for an example input (and that's with a minifier enabled!). 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 ESM: transform all your lodash imports to use lodash-es which is tree-shakable.

Version 6.x introduces a new feature: imports of "modularized" lodash packages, such as lodash.camelcase are rewritten to use optimized imports of lodash or lodash-es. This can significantly reduce bundle size when using third-party dependencies that require these modularized imports: you no longer have to ship copies of the same lodash functions simply because one comes from lodash and another from lodash.camelcase. Applying this to kebabCase saves ~3.5kB after minification.

This input

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

Becomes this output

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

useLodashEs for ES Module Output

While lodash-es is not usable in CommonJS modules, some projects only need ESM output or build both CommonJS and ESM outputs.

In these cases, you can optimize by transforming lodash imports to lodash-es imports:

Your source input

import { isNil } from "lodash";
import kebabCase from "lodash.kebabcase";

CommonJS output

import isNil from "lodash/isNil.js";
import kebabCase from "lodash/kebabCase.js";

ES output (with useLodashEs: true)

import { isNil } from "lodash-es";
import { kebabCase } from "lodash-es";

Individual lodash.* Method Packages

Imports from individual lodash method packages like lodash.isnil or lodash.flattendeep are transformed to use the optimized import path of lodash or lodash-es, consolidating your lodash usage to a single, tree-shakable ESM package.

Your source input

import isNil from "lodash.isnil";
import flattenDeep from "lodash.flattendeep";

CommonJS output

import isNil from "lodash/isNil.js";
import flattenDeep from "lodash/flattenDeep.js";

ES output (with useLodashEs: true)

import { isNil } from "lodash-es";
import { flattenDeep } from "lodash-es";

Aliased local names are supported (import checkNull from "lodash.isnil" becomes import checkNull from "lodash/isNil.js").

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).

parseOptions

Type: Record<string, unknown> | ((id: string) => Record<string, unknown>)
Default: undefined

If defined as a static object, this is passed to rollup's internal parse method. This can be combined with jsx.mode to enable jsx parsing: parseOptions: { jsx: true }

If defined as a function, it is called with the filename. For instance, opt-in to jsx parsing:

parseOptions: (filename) => filename.endsWith(".jsx") ? { jsx: true } : {}

optimizeModularizedImports

Type: boolean
Default: true

When true, imports from individual lodash method packages (e.g., lodash.isnil, lodash.kebabcase) are transformed to optimized imports from lodash or lodash-es.

Set to false if you need to disable this behavior (prior to 6.x, this transformation did not ooccur).

Vite Compatibility

This plugin "just works" as a Vite 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:

A ~23 KiB reduction in compressed size!

Rolldown Compatibility

For basic use, this plugin "just works" with Rolldown. There is a small test suite verifying it.

If you're relying on Rolldown to handle ts/tsx internally, you may need to use parseOptions to configure lang or other parsing options:

optimizeLodashImports({
  // static
  parseOptions: { lang: "ts" },
  // or, dynamically by filename
  parseOptions: (filename) => ({
    lang: filename.endsWith(".ts") ? "ts" : "js",
  }),
});

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);
}

chain() cannot be optimized

The chain() method from lodash cannot be successfully imported from "lodash/chain" without also importing from "lodash". Imports which include chain() are not modified and the plugin prints a warning.

NodeJS 12 and Rollup 2.x / 3.x support

versions of this plugin prior to 5.x supported NodeJS 12 and Rollup 2.x - 3.x. If you need support for these older versions, please use the 4.x release.

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. It also does not modify modularized package imports (lodash.isnil, etc).

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.