Common Errors
Learn to recognize and fix common JavaScript errors like "is not a function", "document is not defined", and module-related issues.

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JavaScript error messages can be cryptic and frustrating, especially when you’re learning.

In this unit, we’ll cover some of the most common JavaScript errors you’ll encounter, explain what causes them, and show you how to fix them.

These are real-world errors that developers face regularly, from “is not a function” to “document is not defined” and module-related issues.

Understanding these errors will save you hours of debugging time and help you write more robust code.

Lessons in this unit:

0: ▶︎ Introduction
1: "X is not a function" errors
2: "document is not defined" error
3: Cannot assign to read only property
4: Parse failure: Unterminated string constant
5: FormData multipart fetch issues
6: regeneratorRuntime is not defined
7: Unexpected identifier in modules
8: Unterminated string literal