Rewrite npm's scripts in JavaScript (#184)

This removes the dependency on `sh` for a Node env. `sh` is not available on Windows

.npm/bin/index.js

@@ -1,14 +1,14 @@
 #!/usr/bin/env node
 
 var spawn = require('child_process').spawn;
-var path = require('path');
+const { getExePath } = require('../get-exe');
 
 var command_args = process.argv.slice(2);
 
 var child = spawn(
-    path.join(__dirname, 'lefthook'),
+    getExePath(),
     command_args,
-    { stdio: [process.stdin, process.stdout, process.stderr] });
+    { stdio: "inherit" });
 
 child.on('close', function (code) {
     if (code !== 0) {

.npm/get-exe.js

@@ -0,0 +1,36 @@
+const path = require("path")
+
+function getExePath() {
+  // Detect OS
+  // https://nodejs.org/api/process.html#process_process_platform
+  let goOS = process.platform;
+  let extension = '';
+  if (['win32', 'cygwin'].includes(process.platform)) {
+    goOS = 'windows';
+    extension = '.exe';
+  }
+
+  // Detect architecture
+  // https://nodejs.org/api/process.html#process_process_arch
+  let goArch = process.arch;
+  switch (process.arch) {
+    case 'x64': {
+      goArch = 'amd64';
+      break;
+    }
+    case 'x32':
+    case 'ia32': {
+      goArch = '386';
+      break;
+    }
+  }
+
+  const dir = path.join(__dirname, 'bin');
+  const executable = path.join(
+    dir,
+    `lefthook_${goOS}_${goArch}`,
+    `lefthook${extension}`
+  );
+  return executable;
+}
+exports.getExePath = getExePath;

.npm/postinstall.js

@@ -1,13 +1,10 @@
-const { spawn } = require("child_process");
-const { join } = require("path");
+if (!process.env.CI) {
+  const { spawnSync } = require('child_process');
+  const { getExePath } = require('./get-exe');
 
-const isCI = process.env.CI;
-
-if (!isCI) {
-  binpath = join(__dirname, 'bin', 'lefthook');
-
-  result = spawn(binpath, ["install", "-f"], {
-      cwd: process.env.INIT_CWD,
-      stdio: [process.stdin, process.stdout, process.stderr]
+  // run install
+  spawnSync(getExePath(), ['install', '-f'], {
+    cwd: process.env.INIT_CWD || process.cwd,
+    stdio: 'inherit',
   });
 }