Node.js v9.0.0 has just been released but the current npm version, npm 5.5.1, does not seem to support it. Consequently, unless you have a specific reason for upgrading Node from its stable v8.9 version, it is probably best to wait a few days until npm makes the change or Node.js fixes the issue.
I’m keeping an eye on this problem and I’ll post more information as soon as there is a positive change.
Note on 11/11/17
Node.js 9.1.0 is out. The problem persists. Here’s a solution:
If you currently have Node.js 9.0.0 or 9.1.0, uninstall it. Windows users, use the regular “uninstall a program” routine to uninstall Node. Then, rename or remove these two folders from your USER/AppData/Roaming folder: npm and npm-cache. Finally, reinstall Node 9.1.0. The npm version that comes with Node should work fine.
p.s. Are you plannig to learn TypeScript or Angular? I have just upgraded my two TypeScript and Angular volumes. You can read more about it here: typescript-plain-language-angular-5/