Add tools/maint/npm_update.py. NFC (#23611)

This script automates the process of updating npm dependencies.

Author: sbc100

tools/maint/npm_update.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+# Copyright 2025 The Emscripten Authors.  All rights reserved.
+# Emscripten is available under two separate licenses, the MIT license and the
+# University of Illinois/NCSA Open Source License.  Both these licenses can be
+# found in the LICENSE file.
+
+"""Update npm dependencies using npm-check-updates
+"""
+
+import os
+import subprocess
+import sys
+
+script_dir = os.path.dirname(os.path.abspath(__file__))
+root_dir = os.path.dirname(os.path.dirname(script_dir))
+
+
+def run(cmd, **args):
+  print('->', ' '.join(cmd))
+  return subprocess.check_output(cmd, text=True, cwd=root_dir, **args)
+
+
+def main():
+  if run(['git', 'status', '-uno', '--porcelain']).strip():
+    print('tree is not clean')
+    #return 1
+
+  output = run(['npx', 'npm-check-updates', '-u'], stderr=subprocess.STDOUT).strip()
+
+  if not run(['git', 'status', '-uno', '--porcelain']).strip():
+    print('no updates')
+    return 0
+
+  message = 'Automatic update of npm dependencies. NFC\n\n'
+  message += 'This change was automatically generated by tools/maint/npm_update.py\n\n'
+  lines = output.splitlines()
+  assert lines[0].startswith('Upgrading ')
+  assert lines[1] == ''
+  assert lines[-1].startswith('Run npm install to install new versions')
+  assert lines[-2] == ''
+  lines = lines[2:-2]
+  message += '\n'.join(lines) + '\n'
+
+  run(['npm', 'install'])
+  run(['git', 'checkout', '-b', 'npm_update'])
+  run(['git', 'add', '-u', 'package.json', 'package-lock.json'])
+  run(['git', 'commit', '-F', '-'], input=message)
+
+
+if __name__ == '__main__':
+  sys.exit(main())