Rails 5 don't precompile JS files with ES6 code in production

Question

I am deploying an app with some javascript that contain ES6 code.

When I did run bundle exec rake assets:precompile RAILS_ENV=production, I got:

ExecJS::RuntimeError: SyntaxError: Unexpected token: punc ())

This is because prueba.js has the following:

var greetings = () => {
  let saludo = 'tio';
  console.log('saludo' + saludo)
};
greetings();

And Uglify don't recognize ES6. For fix this, I had installed and setting the gems:

gem 'sprockets-es6', '~> 0.9.2'
gem 'babel-transpiler', '~> 0.7.0'

But isn't working,

In application.rb, I have:

require "action_view/railtie"
require "sprockets/railtie"
# require "rails/test_unit/railtie"
require 'sprockets/es6'

Note: If i run rake assets:precompile without RAILS_ENV=production, I don't get errors

I think you need to add `.es6` to the file extension for Sprockets to run the JS through babel. — max, Oct 25 '17 at 17:42
@max I changed for a .es6 extension, but I got other error: `ExecJS::RuntimeError: SyntaxError: 'return' outside of function` — Necrogoru, Oct 26 '17 at 14:11

adc · Accepted Answer · 2017-12-08T12:43:49.757

4

When using ES6, if you use uglifier (3.2.0) you can change the file production.rb

with config.assets.js_compressor = Uglifier.new(harmony: true)

edited Dec 08 '17 at 12:43

answered Dec 06 '17 at 11:39

adc

771
4
12

It worked!, just update de Uglifier version, thanks @adcosta – Necrogoru Dec 15 '17 at 16:29
1

Apparently versions above 3.2.0 still show the same error, even with changes mentioned above.. Had to downgrade to 3.2.0 to fix this.. – PragmaticEd Mar 02 '19 at 04:42

score 1 · Answer 2 · edited May 13 '21 at 11:11

1

The accepted answer worked till now but precompile with ES6 and uglifier compression stopped working after the release of new version execjs 2.8 after doing bundle update a few days back.

ERROR: JSON::ParserError: 439: unexpected token at '{"code":"/*! ...

To make it work again just had to fix the version of execjs to 2.7

edited May 13 '21 at 11:11

Dharman

30,962
25
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answered May 13 '21 at 11:05

anoop0302

21
3

I have just upgraded to rails 5.1 and what solve for me was upgrading execjs to 2.8.1 – Natan Rubinstein May 30 '21 at 08:05

Rails 5 don't precompile JS files with ES6 code in production

2 Answers2