"It works fine on my computer!"

"Works on my machine!" has almost become a classic catchphrase for developers to shift blame. Whenever a bug occurs online, especially a front-end issue, this statement can always serve as a universal excuse. But the underlying problems are far more complex than they appear—ranging from environmental differences and dependency version inconsistencies to potential flaws in code logic.

Environmental Differences: The "Gap" Between Local and Production

Discrepancies between development and production environments are a "hotspot" for blame-shifting. The following scenarios are all too common:

1. Node.js Version Mismatch
   Using Node 16 locally while the server runs Node 14 can lead to different API behaviors. For example:

   // Node 16's Array.prototype.at() method throws an error in Node 14
   console.log([1, 2, 3].at(-1)); // Node 14: TypeError
   

2. Browser Feature Support Differences
   Developers test on the latest Chrome version, but users use IE11:

   // Arrow functions throw a syntax error in IE11
   document.addEventListener('click', () => console.log('Clicked'));
   

3. Environment Variables Not Injected Correctly
   For example, process.env.NODE_ENV in a Vue project is development locally but not correctly set to production during build:

   // Mock data that works locally fails online
   if (process.env.NODE_ENV === 'development') {
     useMockData(); // This code might be incorrectly retained in production builds
   }
   

Dependency Versions: The Invisible "Bomb"

A vague version number in package.json can spell disaster:

"dependencies": {
  "lodash": "^4.17.0"  // The ^ symbol can lead to different minor versions being installed on different machines
}

Real-world case: During one build, lodash@4.17.21 was installed, while local testing used 4.17.15, causing inconsistent behavior in _.get() when handling null.

Uncommitted Local Changes: The "Black Hole" of Team Collaboration

# Classic scenario: Forgetting to commit modified config files
git status
# Output: modified: src/config/local.js (but ignored by .gitignore)

Even more insidious are uncommitted local patches:

// Temporary hotfix code forgotten in local
function fetchData() {
  // Temporarily added timeout handling
  return axios.get('/api').timeout(5000); // This line is missing in the online code
}

The Pitfalls of Mock Data

Front-end development often relies on mock data, but real API differences are easily overlooked:

// Ideal mock data returned locally
{
  user: { name: "Test User", age: 25 }
}

// Actual API might return
{
  user: null  // Edge case unhandled
}

The "Magic" of Build Tools

Configuration differences in tools like Webpack or Vite can lead to bizarre issues:

// webpack.config.js local development config
devServer: {
  proxy: {
    '/api': 'http://localhost:3000' // This config doesn't take effect in production builds
  }
}

// Online code directly requests /api, causing CORS errors

"Surprises" from Operating Systems

Path handling differences between Windows and Unix-like systems:

// Path written by a Windows developer
const imagePath = 'src\\assets\\logo.png'; // Errors on a Linux server

// Should use the path module for standardized paths
const path = require('path');
const safePath = path.join('src', 'assets', 'logo.png');

How to Avoid Being the "Blame-Shifter"

1. Standardize Development Environments
   Use Docker or nvm to unify environments:

   nvm use 16.14.0 # Enforce a specific Node version
   

2. Lock Dependency Versions
   Use package-lock.json or yarn.lock, or even consider npm ci for dependency installation.

3. Be Wary of "Local-Only" Code During Reviews
   Pay special attention to environment-related changes:

   - baseURL: 'http://localhost:8080'
   + baseURL: process.env.API_BASE || '/api'
   

4. Set Up a Test Environment Matching Production
   Use docker-compose to simulate real service topologies.

5. Write Defensive Code
   Assume all external dependencies might fail:

   // Trust no environment input
   const apiBase = (process.env.API_BASE || '').replace(/\/$/, '');
   

When Problems Actually Occur

1. Provide Complete Reproduction Steps
   Include:

   - OS: macOS 12.3
   - Browser: Firefox 100.0.2
   - Reproduction Steps:
     1. Click the search box
     2. Triggered when typing Chinese
   

2. Use Screenshots/Videos as Proof
   Avoid arguments like "I can't see it on my end."

3. Check Build Artifact Differences
   Compare file hashes in the dist directory between local and online versions.

4. Minimize Reproduction Code
   Create an isolated CodeSandbox example to pinpoint the issue.