To update all packages that are returned by the npm outdated command to their latest version:

$ npm outdated | tail -n +2 | tr -s ' ' | cut -d ' ' -f1 | xargs -I {} npm up {}

Explaination

npm outdated: Lists all packages installed that are not at their latest version.

tail -n +2: start parsing the output of the previous command from the seccond line (cut off the headers from npm outdated)

tf -s '': since there are varying amounts of whitespace between some of the columns, squeeze it down to just one space between each column

cut -d ' ' -f1: split the previous output into columns on the "space" character and then print the first field

xargs -I {} npm up {}: run the npm up command for each line of the output and replace {} with the actual output (in this case the package name)