Error Reference

A guide to common error messages and their solutions.

Build Errors

Module not found

Error: Cannot find module '@/components/Button'

Cause: The imported file doesn’t exist or path is wrong. Fix:

The import '@/components/Button' can't be found.
Can you check if the file exists and fix the import path?

Unexpected token

SyntaxError: Unexpected token '<'

Cause: JavaScript syntax error, often in JSX. Fix:

Getting a syntax error "Unexpected token".
Can you find and fix the syntax issue?

Type error

Type 'string' is not assignable to type 'number'

Cause: TypeScript type mismatch. Fix:

Getting this type error: [full error message]
Can you fix the type issue?

Export not found

Attempted import error: 'Button' is not exported from './components'

Cause: Component exists but isn’t exported. Fix:

The 'Button' component isn't exported properly.
Can you add the export to the component file?

Runtime Errors

Cannot read properties of undefined

TypeError: Cannot read properties of undefined (reading 'map')

Cause: Trying to use a method on undefined/null value. Fix:

Getting "Cannot read properties of undefined" when mapping over data.
Can you add a check for undefined and handle the empty state?

X is not a function

TypeError: response.json is not a function

Cause: Variable isn’t what you expect. Fix:

Getting "[x] is not a function" error.
Can you check the variable type and fix the function call?

Network error

TypeError: Failed to fetch

Cause: API request failed (network, CORS, or server error). Fix:

API fetch is failing with a network error.
Can you check the API endpoint and error handling?

React Island Errors

These happen inside interactive React components (islands) on your Astro site.

Hydration mismatch

Hydration failed because the initial UI does not match what was rendered on the server

Cause: The static HTML and the hydrated island render different content. Fix:

Getting a hydration mismatch error.
Can you fix the component to render the same on server and client?

Common causes:

Using Date.now() or Math.random() directly
Accessing window or localStorage without checks
Conditional rendering based on browser-only values

Invalid hook call

Invalid hook call. Hooks can only be called inside of the body of a function component

Cause: Hook used incorrectly. Fix:

Getting "Invalid hook call" error.
Can you check that hooks are only used in function components and not inside conditions or loops?

Too many re-renders

Error: Too many re-renders. React limits the number of renders

Cause: Component is in infinite render loop. Fix:

Getting "Too many re-renders" error.
Can you find and fix the infinite loop in the component?

Usually caused by:

Calling setState directly in render
Missing dependency array in useEffect
State update triggering another state update

Database Errors

Permission denied on a row

This action isn't allowed for the current user on table "posts"

Cause: Data is scoped per user, and this operation isn’t permitted for the signed-in user. Fix:

Getting a permission error when [inserting/updating/deleting] data.
Can you check that the data rules let the right users read and write this table?

Foreign key violation

insert or update on table "posts" violates foreign key constraint

Cause: Referenced record doesn’t exist. Fix:

Getting foreign key violation error.
The referenced [table] record doesn't exist.
Can you fix the query or create the referenced record first?

Duplicate key

duplicate key value violates unique constraint

Cause: Trying to insert duplicate value in unique column. Fix:

Getting duplicate key error.
Can you add a check for existing records or use upsert?

Authentication Errors

Session not found

Auth session missing — no signed-in user

Cause: User not logged in or session expired. Fix:

Getting "session missing" error.
Can you add authentication check and redirect to login if not authenticated?

Invalid login credentials

Cause: Wrong email or password. Fix: This is expected for wrong credentials. Ensure your error handling shows a user-friendly message.

Environment Variable Errors

Missing environment variable

Error: Missing environment variable: PUBLIC_API_URL

Cause: Required variable not set. (In Astro, browser-exposed variables are prefixed with PUBLIC_.) Fix:

Go to Settings > Environment
Add the missing variable
Redeploy if in production

Kleap Project settings navigation in English showing Environment Variables — Environment Variables is available under Build in Project settings

Quick Reference Table

Error Contains	Likely Cause	Quick Fix
`Cannot find module`	Wrong import	Check file path
`undefined`	Missing data	Add null check
`not a function`	Wrong variable type	Check variable
`Hydration`	Server/client mismatch	Fix SSR
`Invalid hook`	Hook misuse	Check hook rules
`Too many re-renders`	Infinite loop	Fix useEffect/setState
`not allowed`	Per-user data rule	Check table access rules
`Failed to fetch`	Network/API issue	Check endpoint
`PUBLIC_`	Env var missing	Add to settings

Getting More Help

If an error isn’t listed here:

Copy the full error message
Paste it to Kleap AI with context about what you were doing
Check browser console for additional details

Troubleshooting Guide

Step-by-step solutions to common problems

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Build Errors

Module not found

Unexpected token

Type error

Export not found

Runtime Errors

Cannot read properties of undefined

X is not a function

Network error

React Island Errors

Hydration mismatch

Invalid hook call

Too many re-renders

Database Errors

Permission denied on a row

Foreign key violation

Duplicate key

Authentication Errors

Session not found

Environment Variable Errors

Missing environment variable

Quick Reference Table

Getting More Help

Troubleshooting Guide

​Build Errors

​Module not found

​Unexpected token

​Type error

​Export not found

​Runtime Errors

​Cannot read properties of undefined

​X is not a function

​Network error

​React Island Errors

​Hydration mismatch

​Invalid hook call

​Too many re-renders

​Database Errors

​Permission denied on a row

​Foreign key violation

​Duplicate key

​Authentication Errors

​Session not found

​Invalid login credentials

​Environment Variable Errors

​Missing environment variable

​Quick Reference Table

​Getting More Help

Troubleshooting Guide

Build Errors

Module not found

Unexpected token

Type error

Export not found

Runtime Errors

Cannot read properties of undefined

X is not a function

Network error

React Island Errors

Hydration mismatch

Invalid hook call

Too many re-renders

Database Errors

Permission denied on a row

Foreign key violation

Duplicate key

Authentication Errors

Session not found

Invalid login credentials

Environment Variable Errors

Missing environment variable

Quick Reference Table

Getting More Help