Chapter 272: How to debug any CORS issue

Core Idea

A CORS issue is best debugged with Google Chrome because of the useful error messages.

Key Concepts

• Watch out for Preflight requests
• Set the Access-Control-Allow-Methods header
• Requesting localhost URLs
• Solving any CORS error
• Disable the cache

Code Examples

Access-Control-Allow-Methods: *

• What it demonstrates: Usage pattern for How to debug any CORS issue from the official docs.

Reference Tables

HTTP Method	OPTIONS Request Sent?
GET, HEAD	No
POST	Sometimes*
PUT, DELETE, PATCH, OPTIONS	Yes

Key Takeaways

1. Understand watch out for preflight requests when working with How to debug any CORS issue.
2. Understand set the access-control-allow-methods header when working with How to debug any CORS issue.
3. Understand requesting localhost urls when working with How to debug any CORS issue.
4. Understand solving any cors error when working with How to debug any CORS issue.
5. Understand disable the cache when working with How to debug any CORS issue.

Connects To

• Enametoolong: related page in the Troubleshooting & Errors section.
• Font Picker: related page in the Troubleshooting & Errors section.
• Null: related page in the Troubleshooting & Errors section.