Using some clever instrumentation, I have traced all the calls to mkdirp for the root directory for a module being written by fstream. My gut tells me that it's doing this once for the root directory plus once per file in the source tarball, but that's just intuition. In any case, that directory will be so created by the end of the process.
> /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
1. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at DirWriter._create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/dir-writer.js:35:3)
at /Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:175:15
at /Users/ogd/Documents/projects/npm/npm/node_modules/mkdirp/index.js:29:20
at Object.oncomplete (fs.js:107:15)
2. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
3. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:160:5)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
4. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
5. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
6. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
7. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
8. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
9. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
10. creating /private/var/folders/bf/1f70gl7x2_g0s1dchcrw97xm0000gn/T/node_modules/underscore
at create (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:169:3)
at statCb (/Users/ogd/Documents/projects/npm/npm/node_modules/fstream/lib/writer.js:142:14)
at Object.oncomplete (evalmachine.<anonymous>:107:15)
Using some clever instrumentation, I have traced all the calls to mkdirp for the root directory for a module being written by
fstream. My gut tells me that it's doing this once for the root directory plus once per file in the source tarball, but that's just intuition. In any case, that directory will be so created by the end of the process.