export HTTP_PROXY=http://example.com:1234                                                                                                                                                                                                          
or configure npm proxy via
  npm config set proxy http://example.com:8080                                                                                                                                                                                                       
[email protected] postinstall C:\var\www\project-dir\node_modules\node-sass

node scripts/build.js
Building: C:\Program Files\nodejs\node.exe C:\var\www\project-dir\node_modules\node-gyp\bin\node-gyp.js rebuild --verbose --libsass_ext= --libsass_cflags= --libsass_ldflags= --libsass_library=

gyp info it worked if it ends with ok

gyp verb cli [

gyp verb cli   'C:\Program Files\nodejs\node.exe',

gyp verb cli   'C:\var\www\project-dir\node_modules\node-gyp\bin\node-gyp.js',

gyp verb cli   'rebuild',

gyp verb cli   '--verbose',

gyp verb cli   '--libsass_ext=',

gyp verb cli   '--libsass_cflags=',

gyp verb cli   '--libsass_ldflags=',

gyp verb cli   '--libsass_library='

gyp verb cli ]

gyp info using [email protected]

gyp info using [email protected] | win32 | x64

gyp verb command rebuild []

gyp verb command clean []

gyp verb clean removing "build" directory

gyp verb command configure []

gyp verb check python checking for Python executable "C:\Python37\python.exe" in the PATH

gyp verb which succeeded C:\Python37\python.exe C:\Python37\python.exe

gyp ERR! configure error

gyp ERR! stack Error: Command failed: C:\Python37\python.exe -c import sys; print "%s.%s.%s" % sys.version_info[:3];

gyp ERR! stack   File "", line 1

gyp ERR! stack     import sys; print "%s.%s.%s" % sys.version_info[:3];

gyp ERR! stack                                ^

gyp ERR! stack SyntaxError: invalid syntax

gyp ERR! stack

gyp ERR! stack     at ChildProcess.exithandler (child_process.js:297:12)

gyp ERR! stack     at ChildProcess.emit (events.js:203:13)

gyp ERR! stack     at maybeClose (internal/child_process.js:1021:16)

gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:283:5)

gyp ERR! System Windows_NT 10.0.18362

gyp ERR! command "C:\Program Files\nodejs\node.exe" "C:\var\www\project-dir\node_modules\node-gyp\bin\node-gyp.js" "rebuild" "--verbose" "--libsass_ext=" "--libsass_cflags=" "--libsass_ldflags=" "--libsass_library="

gyp ERR! cwd C:\var\www\project-dir\node_modules\node-sass

gyp ERR! node -v v12.6.0

gyp ERR! node-gyp -v v3.8.0

gyp ERR! not ok

Build failed with error code: 1

npm WARN [email protected] requires a peer of ajv@^6.0.0 but none is installed. You must install peer dependencies yourself.

npm WARN optional SKIPPING OPTIONAL DEPENDENCY: [email protected] (node_modules\fsevents):

npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for [email protected]: wanted {"os":"darwin","arch":"any"} (current: {"os":"win32","arch":"x64"})
npm ERR! code ELIFECYCLE

npm ERR! errno 1

npm ERR! [email protected] postinstall: node scripts/build.js

npm ERR! Exit status 1

npm ERR!

npm ERR! Failed at the [email protected] postinstall script.

npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:

npm ERR!     C:\Users\UserName\AppData\Roaming\npm-cache_logs\2020-03-12T13_15_02_615Z-debug.log
λ npm -v

6.14.2
λ node -v

v12.6.0
          
I have upgraded it via https://github.com/nodejs/node-gyp/wiki/Updating-npm's-bundled-node-gyp
λ npm install -g node-gyp@latest

npm WARN deprecated [email protected]: request has been deprecated, see request/request#3142

C:\Users\UserName\AppData\Roaming\npm\node-gyp -> C:\Users\UserName\AppData\Roaming\npm\node_modules\node-gyp\bin\node-gyp.js
[email protected]

updated 1 package in 7.082s
then I run again same command npm install

but it's still showing following error gyp ERR! node-gyp -v v3.8.0
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@cclauss Thanks for help, issue solved by deleting the node_modules directory and package-lock.json, then run command npm install.
This worked for me as well. 1/9/21.
@cclauss Thanks for help, issue solved by deleting the node_modules directory and package-lock.json, then run command npm install.
This worked for me
I have upgraded it via https://github.com/nodejs/node-gyp/wiki/Updating-npm's-bundled-node-gyp
λ npm install -g node-gyp@latest

npm WARN deprecated [email protected]: request has been deprecated, see request/request#3142

C:\Users\UserName\AppData\Roaming\npm\node-gyp -> C:\Users\UserName\AppData\Roaming\npm\node_modules\node-gyp\bin\node-gyp.js
[email protected]

updated 1 package in 7.082s
then I run again same command npm install

but it's still showing following error gyp ERR! node-gyp -v v3.8.0
Thanks, mate, this works for me.
          
I have tried deleting node-module folder and package-lock.json and running npm build or upgrade still points to node-gyp v3.8.0, although I have v8.1.0 installed. npm config set node-gyp path does not work either.
Any idea why is this?