How to Read Error Messages

Step 1: Don't Panic

The most important thing when you see an error: read it. Most beginners skip the error message and immediately Google the problem. But the error message itself usually tells you exactly what's wrong.

An error message has three parts:

1. Error type — What category of problem (SyntaxError, TypeError, ReferenceError)
2. Error message — A human-readable description of what went wrong
3. Stack trace — Where in your code the error happened

Step 2: Common JavaScript Error Types

| Error Type | Meaning | Common Cause | | ------------------ | -------------------------------------- | -------------------------------------------------- | | SyntaxError | Your code has a grammar mistake | Missing bracket, extra comma, typo | | ReferenceError | You used a variable that doesn't exist | Typo in variable name, forgot to import | | TypeError | You used a value the wrong way | Calling .map() on undefined, wrong argument type | | RangeError | A number is outside the allowed range | Infinite recursion, invalid array length |

Example — ReferenceError:

Step 3: Reading Stack Traces

The stack trace shows the call chain — the path your code took to reach the error. Read it from top to bottom:

Key rules:

• First line with your code = where the bug is (ignore node_modules lines)
• The file path and line number tell you exactly where to look
• Read downward to understand why that code was called

Step 4: TypeScript Errors

TypeScript errors look different — they happen at compile time, before your code runs:

How to read them:

1. File and line — Button.tsx:12:5 means line 12, column 5
2. The rule violated — "Type 'string' is not assignable to type 'number'"
3. The underlined code — The exact expression that's wrong

Common TypeScript errors and fixes:

Step 5: The Error-Reading Workflow

When you hit an error, follow this process every time:

1. Read the error type and message — Don't skip this
2. Find your file in the stack trace — Ignore framework internals
3. Go to the exact line — The file:line reference is clickable in VS Code
4. Check the value — Is something undefined or null that shouldn't be?
5. Check the context — Why was this code called? What was passed in?
6. Fix and re-run — Make one change at a time

Pro tip: In VS Code, hover over red squiggly underlines to see the error message without even running your code.

Step 6: Practice — Spot the Bug

Look at each snippet and identify the error before running it:

Bug 1:

Bug 2:

Bug 3:

What's next? Now that you can read errors, learn How to Use Git for Real Projects to save your work and collaborate with others.