TLDR; Here's why:
The reason this works is because
gulp
tries to run yourgulpfile.js
using your locally installed version ofgulp
, see here. Hence the reason for a global and local install of gulp.
Essentially, when you install gulp
locally the script isn't in your PATH
and so you can't just type gulp
and expect the shell to find the command. By installing it globally the gulp
script gets into your PATH
because the global node/bin/
directory is most likely on your path.
To respect your local dependencies though, gulp
will use your locally installed version of itself to run the gulpfile.js
.