Stack Trace

You might say

The terminal printed a long error. Which line should I send to the AI?

The position list printed when a program fails, ordered from the failure point back to the entryWhen a program crashes and prints a red error in the terminal, the stack trace lists nested function calls leading up to the failure. While the top frame is where execution halted, identifying the first frame that belongs to your own business files points directly to where the bug should be fixed.

Know first

Terminal

Stack Trace

Click each frame to see which line of your code it points to

Terminal

$ node save.js
save.js:24
  return items.map((row) => row);
                 ^
TypeError: Cannot read properties of undefined (reading 'map')

save.jsLine 24

4function handleSave(request) {

5 const items = loadRows(request.file);

6 return items.map((row) => row.total);

7}

22function loadRows(file) {

23 const items = readFile(file);

24 return items.map((row) => row);

25}

This is your own file: items is undefined and line 24 calls .map on it. Start here.

The first error line gives the type and location; the stack lists frames from failure point back to callers. Find your own file's frame before deciding what to fix.

How to read a stack trace

The top frame is where it failed: It shows the exact line and file where the program stopped; the frames below are the callers, layer by layer up to the entry.

Look for your own files only: The trace can mix in runtime and third-party library internals. Only frames from your own files correspond to code you wrote and can be a starting point for a fix.

The error type points at a value: TypeError: Cannot read properties of undefined means some value was empty at that moment; combined with the failing line, it reveals which variable had no value.

Quick checkChoose the best answer

Running the project reports TypeError: Cannot read properties of undefined. The top frame is a Node internal file, and the middle shows at loadRows (save.js:24:21). What should happen next?

Send the whole error to AI without judging anythingFind the frame in your own file, save.js:24, and read that line firstRead only the topmost line because errors always start there

You can say this to an AI Agent

Running node save.js reports TypeError: Cannot read properties of undefined, and the frame at loadRows (save.js:24:21) is in my own file. Read the code near line 24 of save.js first, explain why items is undefined, then rerun to confirm the error is gone.

Learn next

1Server Logs→2Terminal→3Browser DevTools→

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