Correct way to import lodash

import has from 'lodash/has'; is better because lodash holds all it's functions in a single file, so rather than import the whole 'lodash' library at 100k, it's better to just import lodash's has function which is maybe 2k.

If you are using webpack 4, the following code is tree shakable.

import { has } from 'lodash-es';

The points to note;

1. CommonJS modules are not tree shakable so you should definitely use lodash-es, which is the Lodash library exported as ES Modules, rather than lodash (CommonJS).

2. lodash-es's package.json contains "sideEffects": false, which notifies webpack 4 that all the files inside the package are side effect free (see https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free).

3. This information is crucial for tree shaking since module bundlers do not tree shake files which possibly contain side effects even if their exported members are not used in anywhere.

Edit

As of version 1.9.0, Parcel also supports "sideEffects": false, threrefore import { has } from 'lodash-es'; is also tree shakable with Parcel. It also supports tree shaking CommonJS modules, though it is likely tree shaking of ES Modules is more efficient than CommonJS according to my experiment.

Import specific methods inside of curly brackets

import { map, tail, times, uniq } from 'lodash';

Pros:

• Only one import line(for a decent amount of functions)
• More readable usage: map() instead of _.map() later in the javascript code.

Cons:

• Every time we want to use a new function or stop using another - it needs to be maintained and managed

Copied from:The Correct Way to Import Lodash Libraries - A Benchmark article written by Alexander Chertkov.