Troubleshooting Common Vercel Deployment Errors In Next.js

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Deploying a Next.js application to Vercel can sometimes be a smooth process, but occasionally, you might encounter build errors that can be frustrating. In this article, we'll dissect a common Vercel deployment build error scenario, understand the root causes, and provide practical solutions to get your Next.js application up and running. Let's dive in, guys!

Understanding the Build Process

Before we jump into fixing errors, let's quickly recap the Vercel build process. Vercel, a popular platform for deploying web applications, automates much of the deployment workflow. When you push your code to a Git repository connected to Vercel, Vercel detects the changes and initiates a build process. This process typically involves the following steps:

  1. Cloning the Repository: Vercel clones your Git repository to a build machine.
  2. Installing Dependencies: Vercel installs the necessary dependencies specified in your package.json file using a package manager like npm, yarn, or bun.
  3. Building the Application: Vercel runs the build command defined in your package.json file, which usually involves compiling your Next.js application.
  4. Deploying the Application: If the build process is successful, Vercel deploys the built application to its global content delivery network (CDN).

Understanding this process helps us pinpoint where errors might occur.

Analyzing a Common Vercel Build Error

Let's examine a specific Vercel build error scenario. Imagine you're deploying a Next.js application, and you encounter the following error logs:

[21:21:04.914] Running build in Washington, D.C., USA (East) – iad1
[21:21:04.915] Build machine configuration: 2 cores, 8 GB
[21:21:04.956] Cloning github.com/sambulosenda/black-business-portal (Branch: develop, Commit: 955eca9)
[21:21:05.359] Cloning completed: 403.000ms
[21:21:07.963] Restored build cache from previous deployment (Ak4enyV3V1rHfrcvo9Z1Ncw7z7fS)
[21:21:10.510] Running "vercel build"
[21:21:10.991] Vercel CLI 44.4.3
[21:21:11.330] Running "install" command: `bun install`...
[21:21:11.369] bun install v1.2.18 (0d4089ea)
[21:21:11.514]
[21:21:11.517] $ prisma generate
[21:21:13.120] Prisma schema loaded from prisma/schema.prisma
[21:21:13.870]
[21:21:13.870] ✔ Generated Prisma Client (v6.9.0) to ./node_modules/@prisma/client in 371ms
[21:21:13.870]
[21:21:13.871] Start by importing your Prisma Client (See: https://pris.ly/d/importing-client)
[21:21:13.871]
[21:21:13.871] Tip: Interested in query caching in just a few lines of code? Try Accelerate today! https://pris.ly/tip-3-accelerate
[21:21:13.871]
[21:21:14.206]
[21:21:14.208] Checked 564 installs across 643 packages (no changes) [2.86s]
[21:21:14.213] Detected Next.js version: 15.3.3
[21:21:14.213] Running "bun run build"
[21:21:14.219] $ prisma generate && next build
[21:21:14.845] Prisma schema loaded from prisma/schema.prisma
[21:21:15.556]
[21:21:15.557] ✔ Generated Prisma Client (v6.9.0) to ./node_modules/@prisma/client in 374ms
[21:21:15.558]
[21:21:15.558] Start by importing your Prisma Client (See: https://pris.ly/d/importing-client)
[21:21:15.558]
[21:21:15.558] Tip: Want to turn off tips and other hints? https://pris.ly/tip-4-nohints
[21:21:15.558]
[21:21:15.582] ┌─────────────────────────────────────────────────────────┐
[21:21:15.582] │  Update available 6.9.0 -> 6.12.0                       │
[21:21:15.582] │  Run the following to update                            │
[21:21:15.582] │    npm i --save-dev prisma@latest                       │
[21:21:15.582] │    npm i @prisma/client@latest                          │
[21:21:15.582] └─────────────────────────────────────────────────────────┘
[21:21:16.544]    ▲ Next.js 15.3.3
[21:21:16.545]
[21:21:16.586]    Creating an optimized production build ...
[21:21:34.198]  ✓ Compiled successfully in 13.0s
[21:21:34.202]    Linting and checking validity of types ...
[21:21:46.490]
[21:21:46.491] Failed to compile.
[21:21:46.491]
[21:21:46.491] ./src/app/forgot-password/page.tsx
[21:21:46.491] 20:9  Error: 'router' is assigned a value but never used.  @typescript-eslint/no-unused-vars
[21:21:46.491] 77:38  Error: `'` can be escaped with `'`, `‘`, `'`, `’`.  react/no-unescaped-entities
[21:21:46.492] 93:25  Error: `'` can be escaped with `'`, `‘`, `'`, `’`.  react/no-unescaped-entities
[21:21:46.492] 179:29  Error: `'` can be escaped with `'`, `‘`, `'`, `’`.  react/no-unescaped-entities
[21:21:46.492] 179:98  Error: `'` can be escaped with `'`, `‘`, `'`, `’`.  react/no-unescaped-entities
[21:21:46.492]
[21:21:46.492] ./src/app/reset-password/page.tsx
[21:21:46.492] 224:37  Error: `'` can be escaped with `'`, `‘`, `'`, `’`.  react/no-unescaped-entities
[21:21:46.492]
[21:21:46.492] info  - Need to disable some ESLint rules? Learn more here: https://nextjs.org/docs/app/api-reference/config/eslint#disabling-rules
[21:21:46.504] error: script "build" exited with code 1
[21:21:46.521] Error: Command "bun run build" exited with 1
[21:21:46.962]
[21:21:49.841] Exiting build container

This log output provides valuable information about what went wrong during the build process. Let's break it down and identify the key issues.

Key Observations

  1. Build Environment: The build is running in Vercel's environment, using a machine with 2 cores and 8 GB of memory.
  2. Repository Cloning: Vercel successfully cloned the Git repository from github.com/sambulosenda/black-business-portal.
  3. Dependency Installation: The build process uses bun install to install dependencies, and it appears to complete successfully.
  4. Prisma Integration: The application uses Prisma, an ORM, and the Prisma client is generated without issues.
  5. Next.js Build: The Next.js build process starts, and the application compiles successfully in 13 seconds.
  6. Linting and Type Checking: The build process includes linting and type checking, which is where the errors occur.
  7. ESLint Errors: The build fails due to ESLint errors in the src/app/forgot-password/page.tsx and src/app/reset-password/page.tsx files.
  8. Error Messages: The error messages indicate two main issues:
    • @typescript-eslint/no-unused-vars: A variable (router) is assigned a value but never used.
    • react/no-unescaped-entities: Apostrophes (') are not properly escaped in JSX.
  9. Build Exit Code: The build script exits with code 1, indicating a failure.

Root Causes

Based on the error messages, the root causes of the build failure are:

  1. Unused Variable: The @typescript-eslint/no-unused-vars ESLint rule is triggered because the router variable is declared but not used in the forgot-password/page.tsx file. This is a common issue that can be easily fixed by either using the variable or removing it.
  2. Unescaped Apostrophes: The react/no-unescaped-entities ESLint rule is triggered because apostrophes (') are used in JSX without proper escaping. In JSX, certain characters like ', ", <, >, and & need to be escaped to avoid potential rendering issues and security vulnerabilities.

Solutions to Fix the Errors

Now that we understand the errors, let's explore how to fix them.

1. Addressing the Unused Variable Error

The @typescript-eslint/no-unused-vars error is straightforward to fix. You have two options:

  • Use the Variable: If the router variable is intended to be used, ensure that it is used within the component's logic. For example, you might use it to navigate to a different page.
  • Remove the Variable: If the router variable is not needed, simply remove its declaration from the component.

Here's an example of how to fix the error by removing the unused variable:

// src/app/forgot-password/page.tsx

import React from 'react';

const ForgotPasswordPage: React.FC = () => {
  // ... other code
  
  // Remove the unused router variable
  // const router = useRouter();

  return (
    // ... JSX content
  );
};

export default ForgotPasswordPage;

By removing the unused variable, you eliminate the ESLint error and allow the build to proceed.

2. Fixing Unescaped Apostrophes

The react/no-unescaped-entities error requires you to properly escape apostrophes in your JSX code. There are several ways to do this:

  • Use HTML Entities: Replace the apostrophe (') with its HTML entity &apos; or &#39;.
  • Use Template Literals: Enclose the text containing the apostrophe in template literals (`).

Here's an example of how to fix the error using HTML entities:

// src/app/forgot-password/page.tsx

import React from 'react';

const ForgotPasswordPage: React.FC = () => {
  return (
    <div>
      <p>This is an example of escaping an apostrophe using &apos;.</p>
      <p>This is another example using &#39;.</p>
    </div>
  );
};

export default ForgotPasswordPage;

Here's an example of how to fix the error using template literals:

// src/app/forgot-password/page.tsx

import React from 'react';

const ForgotPasswordPage: React.FC = () => {
  return (
    <div>
      <p>{`This is an example of escaping an apostrophe using template literals.`}</p>
    </div>
  );
};

export default ForgotPasswordPage;

Choose the method that best suits your coding style and apply it consistently throughout your application. By escaping apostrophes, you prevent potential rendering issues and security vulnerabilities.

Best Practices for Avoiding Build Errors

To minimize the chances of encountering build errors in your Vercel deployments, consider adopting these best practices:

  1. Linting and Formatting: Integrate ESLint and Prettier into your development workflow to automatically catch and fix code style issues. This helps ensure code consistency and prevents common errors from making their way into your deployments.
  2. Type Checking: Use TypeScript to add static typing to your Next.js application. TypeScript can catch type-related errors early in the development process, reducing the likelihood of runtime errors and build failures.
  3. Testing: Write unit tests and integration tests to verify the correctness of your code. Automated tests can help you identify bugs and regressions before they impact your users.
  4. Environment Variables: Use environment variables to manage configuration settings that vary between environments (e.g., development, staging, production). Ensure that all necessary environment variables are set in your Vercel project settings.
  5. Dependency Management: Keep your dependencies up to date and use semantic versioning to manage dependencies effectively. Regularly audit your dependencies for security vulnerabilities and update them as needed.
  6. Vercel CLI: Use the Vercel CLI to preview and test your deployments locally before pushing them to production. This allows you to catch errors early and iterate quickly.
  7. Review Build Logs: When a build fails, carefully review the Vercel build logs to identify the root cause of the error. The logs often provide valuable information about what went wrong and how to fix it.

Conclusion

Vercel deployment build errors can be a hurdle, but by understanding the build process and common error patterns, you can effectively troubleshoot and resolve them. In this article, we analyzed a specific build error scenario, identified the root causes (unused variables and unescaped apostrophes), and provided practical solutions to fix them. By adopting best practices like linting, type checking, and testing, you can minimize the chances of encountering build errors and ensure smooth deployments of your Next.js applications. So, next time you face a build error, don't panic – you've got this!

Remember, debugging is a skill, and every error you encounter is an opportunity to learn and improve. Keep coding, keep deploying, and keep building amazing things!