Command "npm update" vs package "npm-check-updates"

What is the difference between the command npm update and the package npm-check-updates? Is it fully safe to use the latter?

It seems after executing npm update not all packages are updated, thus it seem it is incomplete. Many other popular SO answers refer to use first the prior command and then the latter, but I still do not understand what the latter does that the prior does not.

A bit late to the party but I felt like the previously accepted answer is outdated and slightly lacking.

What npm Offers

npm update - updates the dependencies both in package.json and package-lock.json in accordance to the semantic version rules defined in package.json.

Key features of npm update:

• It will never update to a breaking version.
• (npm@7 and above) You can choose to update only the package.json file with npm update --package-lock false. However, this flag will completely ignore package-lock.json and hence automatic pruning of extraneous modules will also be disabled.
• (npm@7 and above) You can see the changes npm update will perform with the flag --dry-run, without actually updating.

npm outdated - shows all the packages that have newer versions available, this includes breaking changes. It prints a table that includes the package, the current version, the wanted version - according to the semver rules in the package.json - the latest version and the location of the package.

What npm-check-updates Offers

Running ncu without any flags will print a list of all the outdated packages and the version to which it would update, but will not apply any changes.

ncu --update - apply changes to the package.json file only. It will change the versions of all the dependencies in package.json to the latest (even if it's a breaking version!), but will not modify the package-lock.json file. For that, you will need to run npm install.

ncu --target [patch, minor, latest, newest, greatest] - choose which type of version to list/update.

npm vs. ncu