problem

① Update the version of macOS Catalina to 10.15.4

② Rails s in the directory of the application currently being produced

③ I get the following error

Could not find a JavaScript runtime. See https://github.com/rails/execjs for a list of available runtimes. (ExecJS::RuntimeUnavailable)

Solution

https://nodejs.org/ja/download/current/

Whether to install the latest version of Node.js at the above site

Install using homebrew in the terminal

% brew install nodejs

Then, I was able to start the local server with rails s safely.