Hey there, let's break this down step by step—this is a super common gotcha when inheriting legacy Node.js apps with missing docs, so you're not alone here.

First, Get the Full Error Details #

The truncated PM2 error log you shared only tells half the story. Let's get the full context to pinpoint the issue:

• Run pm2 logs <your-app-id-or-name> to see the complete error trace—this will show you exactly which file and line is throwing the syntax error.
• Skip PM2 entirely for a moment and run the app directly with Node: node /path/to/your/apps/entry-file.js. This often gives clearer, untruncated error messages that are easier to debug.

Common Causes & Fixes #

1. Node.js Version Mismatch #

This is the #1 culprit for this specific error. If the previous dev used modern ES6+ syntax (like optional chaining ?., nullish coalescing ??, or top-level await) but your server's PM2 is using an older Node version that doesn't support those features, you'll get this token error.

• Check which Node version PM2 is using: Run pm2 env <app-id> and look for the NODE_VERSION entry.
• Compare it to the syntax in your code: For example, optional chaining requires Node 14.0+, nullish coalescing needs Node 14.0+, and top-level await needs Node 14.8+.
• Fix options:
  • Upgrade Node.js on your server to match the version the app was built for.
  • If you can't upgrade Node, add Babel to transpile modern syntax down to compatible code.
  • Specify a custom Node binary in your ecosystem.json (if you have multiple Node versions installed):

    {
      "apps": [{
        "name": "your-app",
        "script": "app.js",
        "env": {
          "NODE_BIN_PATH": "/usr/local/bin/node16" // Replace with your correct path
        }
      }]
    }
    

2. Invalid File Encoding #

Occasionally, files saved with UTF-16 encoding or a Byte Order Mark (BOM) will cause Node to throw unexpected token errors, even if the syntax looks correct.

• On Linux/macOS, check the file encoding with: file -i /path/to/your/entry-file.js. Look for charset=utf-8 (no BOM).
• On VS Code, check the encoding in the bottom-right corner—if it says UTF-8 with BOM, click it and select "Save with Encoding > UTF-8".

3. Syntax Typos or Unsupported Syntax #

Double-check the file/line from your full error log for:

• Accidental use of Chinese/non-ASCII punctuation (like “ instead of ", ； instead of ;). These are invisible at a glance but break Node's parser.
• Missing brackets, parentheses, or semicolons that create invalid syntax.
• Experimental syntax (like decorators) that hasn't been transpiled or enabled with Node flags.

4. PM2 Configuration Issues #

Make sure your ecosystem.json is pointing to the correct entry file:

• Verify the script field path is accurate (relative or absolute). If PM2 is trying to load a non-JS file or a corrupted file, you'll get this error.
• Try simplifying the config temporarily to rule out complex settings:

  {
    "apps": [{
      "name": "your-app",
      "script": "./app.js", // Double-check this path!
      "watch": false
    }]
  }
  

Quick Debugging Checklist #

1. Run the app directly with Node (not PM2) to confirm if the error is app-specific or PM2-related.
2. Match the Node version PM2 uses to the version required by your app's syntax.
3. Check the problematic file's encoding and fix any non-ASCII punctuation.
4. Validate your ecosystem.json for typos or incorrect paths.

Been there, inherited a Node app where the previous dev used Node 16 syntax but the server was stuck on Node 12—spent hours chasing this until I checked the PM2 env. Hope this gets you up and running!

内容的提问来源于stack exchange，提问作者eazybob