rollup-plugin-optimize-lodash-imports v1.0.2

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";
import isString from "lodash/isString";
import padStartFp from "lodash/fp/padStart";

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";

ES output (with useLodashEs: true)

import { isNil } from "lodash-es";

Usage

import optimizeLodashImports from "rollup-plugin-optimize-lodash-imports";

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!

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 Rollup will print a warning.

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.