As of npm v8, you can pass --save to npm update, which will update the versions of everything in package.json.

After using npm outdated -p and cut for so long, I was surprised when someone pointed this out to me.

It just updates the minor versions, but that's usually what I want — if I try to update all the major versions, the chances that everything is compatible with everything is usually pretty low, so I have to do that fairly piecemeal.