Performance: Running npm on Windows runs node executable twice (which is slow), to find the prefix

[jakub-g]

I'm not sure if this is feasible / easy to optimize, but when profiling some of our scripts, I noticed the following:

As a Windows user, when I run npm through git bash in my shell [1], or have a JS script which uses child_process.spawn() which calls npm run something, I expect that node executable will be run only once as a result of such command.

• [1] https://github.com/npm/cli/blob/v7.9.0/bin/npm#L23
• [2] https://github.com/npm/cli/blob/v7.9.0/bin/npm.cmd#L12

However, invoking npm in both cases (either through Windows .cmd or git bash compatible .sh) runs npm prefix -g internally.

So every time any npm command is run, the penalty of booting up a node.exe executable happens twice (on my Dell machine it's about 600-700ms).

It's not a huge issue in itself, but when relying on scripts in package.json, especially when those scripts are compounded (i.e. npm run x calls npm run y), this penalty of multiple node executable calls accumulates fast.

Current Behavior:

Running npm through terminal or spawn runs node.exe twice, incurring the penalty of node.exe boot twice

Expected Behavior:

Running npm should ideally run node.exe only once.

Or at least, in case of nested invocations, there could be perhaps some optimization: 2nd and further calls to npm could reuse an env var exported by the first, top-level npm invocation? (i.e. avoid calling npm prefix -g more than once per lifetime of a top-level script)

(Although I know it can be tricky to rely on the env var, because some script may change it at runtime and break things).

Steps To Reproduce:

1. Create a file C:\git\node_debug\index.js with following contents:

require('fs').writeFileSync(`${__dirname}/tmp_${Date.now()}`, `${process.argv.join(' ')}\r\n`)

2. Run npm through git bash using NODE_OPTIONS to run the hook above on each node.exe creation:

NODE_OPTIONS='--require C:\git\node_debug\index.js' npm

3. Observe that two temp files were written to disk in C:\git\node_debug

Environment:

Windows 10 (git bash), node@12.22.1, npm@6.14.12 (but behavior will be same with npm@7.9.0 as it calls npm prefix -g too)

[milaninfy]

Closing: This is fixed by #7271