How to import date-fns JS library to Rails project using yarn

Question

I try to import date-fns lib using yarn to Rails project, but it didn't work.

I use yarn to install date-fns :

yarn add date-fns

After install them I try to import this lib to app/javascript/packs/application.js file, but it didn't work:

// This file is automatically compiled by Webpack, along with any other files
// present in this directory. You're encouraged to place your actual application logic in
// a relevant structure within app/javascript and only use these pack files to reference
// that code so it'll be compiled.
//

import 'core-js/stable';
import 'regenerator-runtime/runtime';
import format from "date-fns/format";

I got an error:

> format(new Date(2014, 1, 11), 'yyyy-MM-dd')
> VM498:1 Uncaught ReferenceError: format is not defined
    at <anonymous>:1:1

If I try import it using app/assets/javascripts/application.js file:

//= require jquery3
//= require jquery_ujs
//= require popper
//= require bootstrap
//= require date-fns/format

console.log("date-fns", format(new Date(2014, 1, 11), "yyyy-MM-dd"));

It seems the library is connected, so I can call the method format , but I got another error:

> Uncaught ReferenceError: exports is not defined
# refers to this line 
>  Object.defineProperty(exports, "__esModule", {
>   value: true
>  });
> exports.default = format;

# and 

> Uncaught TypeError: Cannot read property 'default' of undefined
# refers to this line 
> function format(dirtyDate, dirtyFormatStr, dirtyOptions) {
>  (0, _index10.default)(2, arguments);

What am I doing wrong?

Answer 1

The way to import a library in Webpack and Rails is to install it via yarn, as you did, and then require it in the application pack.

# console
$ yarn add date-fns

# app/javascript/packs/application.js
require("date-fns")