Please give more Information: "System information (as much as possible)"

Do you use the latest git version? Can you tell use the commit id?

If so its possible that you have to run composer und npm

See #21277

folder libraries/vendor is empty maybe this is the problem

It certainly is.

What can i do? What script should i run?

need to install dependacies: composer install if I right understood (see https://docs.joomla.org/J4.x:Setting_Up_Your_Local_Environment)

but still an errors:
at admin login: Class 'Joomla\Module\Login\Administrator\Helper\LoginHelper' not found
at frontend: Class 'Joomla\Module\Menu\Site\Helper\MenuHelper' not found

Download composer and npm

Run composer install and i think npm Install.

@rdeutz could give the correct commands?

Ok i test this.

okay so if you had previously installed Joomla 4-dev repo, you have to reinstall everything from the beginning:

• Update your local Joomla 4-dev repo
• Remove /libraries/autoload_psr4.php manually
• Remove /configuration.php
• Follow https://docs.joomla.org/J4.x:Setting_Up_Your_Local_Environment , basically just need:
  • composer install
  • npm install
  • npm run build:css
  • npm run build:js
• Install Joomla again

upd: the frontend error remains Class 'Joomla\Module\Menu\Site\Helper\MenuHelper' not found

I got best results using the commands in the build.php file:

So

• composer install --no-dev --no-autoloader --ignore-platform-reqs
• npm install --unsafe-perm

I also found it needs at least Node JS version 8. Version 6 doesn't work.
You don't need to run npm run build commands. Those are already run by the npm install command.
You also don't necessary need to delete the configuration.php file. Onyl when you want to do a fresh installation.

I also found it needs at least Node JS version 8. Version 6 doesn't work.

The required Node/NPM versions are also specified in the package.json file after #21219 so it's not like this is buried anywhere either (basically it's NPM 5.6 and the oldest Node LTS, 8.9.4, which comes bundled with that, anything earlier has quirks with the package-lock.json file).

Tried with fresh git clone

composer install
runs fine

but with
npm install

some packages fail:
jquery-minicolors
LeaVerou/awesomplete
webcomponents/webcomponentsjs/2.0.3

npm http 404 http://registry.npmjs.org/claviska/jquery-minicolors/2.2.6
npm ERR! Error: No dist in undefined package
npm ERR! at next (C:\program files (x86)\nodejs\node_modules\npm\lib\cache.js:746:26)
npm ERR! at C:\program files (x86)\nodejs\node_modules\npm\lib\cache.js:739:5
npm ERR! at saved (C:\program files (x86)\nodejs\node_modules\npm\node_modules\npm-registry-client\lib\get.js:142:7)
npm ERR! at Object.oncomplete (fs.js:107:15)
npm ERR! If you need help, you may report this log at:
npm ERR! http://github.com/isaacs/npm/issues
npm ERR! or email it to:
npm ERR! npm-@googlegroups.com

npm ERR! System Windows_NT 6.2.9200
npm ERR! command "C:\program files (x86)\nodejs\node.exe" "C:\program files (x86)\nodejs\node_modules\npm\bin\npm-cli.js" "install"
npm ERR! cwd D:\xampp\htdocs\devel\joomla-cms4
npm ERR! node -v v0.10.13
npm ERR! npm -v 1.3.2

npm http 404 http://registry.npmjs.org/webcomponents/webcomponentsjs/2.0.3

npm ERR! Failed resolving git HEAD (git://github.com/LeaVerou/awesomplete) fatal: ambiguous argument 'master': unknown revision or path not in the working tree.
npm ERR! Failed resolving git HEAD (git://github.com/LeaVerou/awesomplete) Use '--' to separate paths from revisions, like this:
npm ERR! Failed resolving git HEAD (git://github.com/LeaVerou/awesomplete) 'git [...] -- [...]'
npm ERR! Failed resolving git HEAD (git://github.com/LeaVerou/awesomplete)

@ggppdk Did you try with npm install --unsafe-perm? I had some strange errors on Linux without that parameter as well.

yes tried
npm install --unsafe-perm

which did not work,
and i solved it with

npm config set strict-ssl false
npm install 

or

npm config set registry="http://registry.npmjs.org/"
npm install 

then after solving perms issues i get 2 not found errors (404)
npm http 404 http://registry.npmjs.org/claviska/jquery-minicolors/2.2.6
npm http 404 http://registry.npmjs.org/webcomponents/webcomponentsjs/2.0.3

and for 1 more error for
git://github.com/LeaVerou/awesomplete
fatal: ambiguous argument 'master': unknown revision or path not in the working tree.

OK, i confused V8 JavaScript engine with the version of node JS
which options appeared when using --help

I had old Node.js version
I have updated Node.js to v8.11.3 x64 for windows

and npm install completed without errors

Now i can go through installation of J4 without anything missing ...

Closed