[javascript] Correct way to import lodash

I had a pull request feedback below, just wondering which way is the correct way to import lodash?

You'd better do import has from 'lodash/has'.. For the earlier version of lodash (v3) which by itself is pretty heavy, we should only import a specidic module/function rather than importing the whole lodash library. Not sure about the newer version (v4).

import has from 'lodash/has';

vs

import { has } from 'lodash';

Thanks

You can import them as

import {concat, filter, orderBy} from 'lodash';

or as

import concat from 'lodash/concat';
import orderBy from 'lodash/orderBy';
import filter from 'lodash/filter';

the second one is much optimized than the first because it only loads the needed modules

then use like this

pendingArray: concat(
                    orderBy(
                        filter(payload, obj => obj.flag),
                        ['flag'],
                        ['desc'],
                    ),
                    filter(payload, obj => !obj.flag),

I just put them in their own file and export it for node and webpack:

// lodash-cherries.js
module.exports = {
  defaults: require('lodash/defaults'),
  isNil: require('lodash/isNil'),
  isObject: require('lodash/isObject'),
  isArray: require('lodash/isArray'),
  isFunction: require('lodash/isFunction'),
  isInteger: require('lodash/isInteger'),
  isBoolean: require('lodash/isBoolean'),
  keys: require('lodash/keys'),
  set: require('lodash/set'),
  get: require('lodash/get'),
}

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.

If you are using babel, you should check out babel-plugin-lodash, it will cherry-pick the parts of lodash you are using for you, less hassle and a smaller bundle.

It has a few limitations:

• You must use ES2015 imports to load Lodash
• Babel < 6 & Node.js < 4 aren’t supported
• Chain sequences aren’t supported. See this blog post for alternatives.
• Modularized method packages aren’t supported

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.