I had this error message TypeError: Cannot read properties of undefined (reading 'length') before in my code many times before and it usually means that the you're trying to access data from an object that does not yet exist in memory.

In your code that you posted, the line that is causing the error is likely to be:

const itens = db.all().map(item => `ID: ${item.ID} | QUANTIDADE: ${item.data.conta.length || "0"}`)

Since you're not properly checking to see if it exists before outputting data. I see you're using a logical OR for this but sometimes that doesn't properly work as expected.

To fix this, replace the check with a ternary operator to see if item.data is defined before accessing its properties. You can modify the line to look something like this:

const itens = db.all().map(item => `ID: ${item.ID} | QUANTIDADE: ${item.data && item.data.conta ? item.data.conta.length : "0"}`)

This checks to see if item.data exists and if it has the conta property before accessing its length. If either of these properties is resolved as being undefined, it will default to "0".

Answer from Joe on Stack Overflow
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GitHub
github.com › cvat-ai › cvat › issues › 8365
"Cannot read properties of undefined (reading 'length')" when returning serverless predictions · Issue #8365 · cvat-ai/cvat
August 28, 2024 - But in CVAT when I use it as an interactor to get masks or points, I get Interaction error occurred - Cannot read properties of undefined (reading 'length')
Author: cvat-ai
Discussions

Possible interactor return types (masks)
I am creating my own MedSAM2-related ... when I want ot useit in interactor mode, it gives me an error in the CVAT frontend: Interaction error occurred Cannot read properties of undefined (reading 'length')... More on github.com
🌐 github.com
2
December 8, 2025
TypeError: Cannot read properties of undefined (reading 'length') unhandledRejection
I had this error message TypeError: Cannot read properties of undefined (reading 'length') before in my code many times before and it usually means that the you're trying to access data from an object that does not yet exist in memory. More on stackoverflow.com
🌐 stackoverflow.com
Could not upload annotation
Actions before raising this issue I searched the existing issues and did not find anything similar. I read/searched the docs Steps to Reproduce Create a new project. Enter a name (test) for the pro... More on github.com
🌐 github.com
5
February 27, 2024
SAM3 integrate
Actions before raising this issue I searched the existing issues and did not find anything similar. I read/searched the docs Steps to Reproduce I tried to integrate the SAM3 model following the SAM output example, and encountered the iss... More on github.com
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1
April 26, 2026
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TrackJS
trackjs.com › javascript answers › how to fix `cannot read properties of undefined (reading 'length')`
How to fix `Cannot read properties of undefined (reading 'length')` • TrackJS
April 8, 2026 - Common JavaScript error when accessing length property on undefined values. Usually occurs with arrays, strings, or API responses that haven't loaded yet. Quick fixes: add null checks, use optional chaining, handle loading states.
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GitHub
github.com › cvat-ai › cvat › issues › 10088
Possible interactor return types (masks) · Issue #10088 · cvat-ai/cvat
December 8, 2025 - I am creating my own MedSAM2-related ... when I want ot useit in interactor mode, it gives me an error in the CVAT frontend: Interaction error occurred Cannot read properties of undefined (reading 'length')...
Author: cvat-ai
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GitHub
github.com › cvat-ai › cvat › issues › 7527
Could not upload annotation · Issue #7527 · cvat-ai/cvat
February 27, 2024 - The error that we constantly receive: Could not upload annotation for the [task 528524] (https://app.cvat.ai/tasks/528524) Cannot read properties of undefined (reading 'attributes') cvat-ui.ec77c400e46942ed8d77.min.js:2 Uncaught TypeError: Cannot read properties of undefined (reading 'attributes') at wi.appendDefaultAttributes (cvat-ui.ec77c400e46942ed8d77.min.js:2:2801171) at new bi (cvat-ui.ec77c400e46942ed8d77.min.js:2:2798369) at new wi (cvat-ui.ec77c400e46942ed8d77.min.js:2:2814852) at Xi.import (cvat-ui.ec77c400e46942ed8d77.min.js:2:2843733) at mo (cvat-ui.ec77c400e46942ed8d77.min.js:2:2873707) at async No.e.annotations.clear.implementation (cvat-ui.ec77c400e46942ed8d77.min.js:2:2883891) at async Ca.apiWrapper (cvat-ui.ec77c400e46942ed8d77.min.js:2:2610028) at async Ca.clear (cvat-ui.ec77c400e46942ed8d77.min.js:2:2749919) at async cvat-ui.ec77c400e46942ed8d77.min.js:2:8116485 ·
Author: cvat-ai
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New Releases
newreleases.io › project › github › cvat-ai › cvat › release › v2.13.0
cvat-ai/cvat v2.13.0 on GitHub
May 9, 2024 - Cannot read properties of undefined (reading 'addClass') (#7834) Fixed exception 'Could not read property length of undefined' when copy/paste a skeleton point (#7843)
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GitHub
github.com › cvat-ai › cvat › pull › 7421
Fixed "Cannot read properties of undefined (reading 'toLowerCase')" by bsekachev · Pull Request #7421 · cvat-ai/cvat
Motivation and context We have many exceptions like this: Cannot read properties of undefined (reading 'toLowerCase') on app.cvat.ai It happens because event.code property has undefined value. It i...
Author: cvat-ai
Find elsewhere
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GitHub
github.com › cvat-ai › cvat › issues › 10529
SAM3 integrate · Issue #10529 · cvat-ai/cvat
April 26, 2026 - I tried to integrate the SAM3 model following the SAM output example, and encountered the issue 'Cannot read properties of undefined (reading 'length')' at the end. May I ask how to solve this problem?
Author: cvat-ai
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GitHub
github.com › cvat-ai › cvat › pull › 9095
Fix: Cannot read properties of undefined (reading 'width') in Video GT job by klakhov · Pull Request #9095 · cvat-ai/cvat
It seems that a regression was introduced during recent refactoring related to frame metadata. In a GT job created from a video, navigating through frames results in an error: *Cannot read properties of undefined (reading 'width').
Author: cvat-ai
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GitHub
github.com › cvat-ai › cvat › issues › 7861
Semi automatic annotation Skeleton w/ Mediapipe : TypeError Cannot read properties of undefined (reading 'attr') · Issue #7861 · cvat-ai/cvat
May 7, 2024 - Semi automatic annotation Skeleton ... read properties of undefined (reading 'attr')#7861 ... I searched the existing issues and did not find anything similar. ... Use the provided function.yaml and main.py files to set up a Nuclio function. Call the annotate function. ... Semi automatic annotation for right hand using media pipe, similar to open pose skeleton annotation but with media pipe ... I'm trying to use media pipe and cvat for semi automatic ...
Author: cvat-ai
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Stack Overflow
stackoverflow.com › questions › 46059064 › opencv-typeerror-cannot-read-property-length-of-undefined
opencv - TypeError: Cannot read property 'length' of undefined
cv.readImage("./examples/files/mona.png", function(err, im){ im.detectObject(cv.FACE_CASCADE, {}, function(err, faces){ for (var i=0;i<faces.length; i++){ var x = faces[i] im.ellipse(x.x + x.width/2, x.y + x.height/2, x.width/2, x.height/2); } im.save('./out.jpg'); }); }) ... I believe your faces object is undefined (#noSh!t) because you might have an error in the err object from the callback.
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GitHub
github.com › cvat-ai › cvat › issues › 5281
JS Error After Importing Annotation Using API · Issue #5281 · cvat-ai/cvat
November 11, 2022 - Searched past issues I imported the annotation using python in the format asked in the API. I am using CVAT local · I imported the annotations using API but the server gave me "TypeError Cannot read properties of undefined (reading 'id')", The format of the object imported is correct
Author: cvat-ai
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GitHub
github.com › cvat-ai › cvat › issues › 8177
Unable to upload video to a cvat task · Issue #8177 · cvat-ai/cvat
July 16, 2024 - Started CVAT, and tried to upload a video file. Error message when trying to access Project: TypeError Cannot read properties of undefined (reading 'message')
Author: cvat-ai
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Reddit
reddit.com › r/foundryvtt › typeerror: cannot read properties of undefined (reading 'length')
r/FoundryVTT on Reddit: TypeError: Cannot read properties of undefined (reading 'length')
May 6, 2024 -

Receiving this error on one of my game files. All mods are turned off currently.

Currently running Version 11 Build 315

DnD5e 3.1.2

foundry.js:68326 Cannot read properties of undefined (reading 'length')

|| || ||fetch|@|foundry.js:68326| ||notify|@|foundry.js:68223| ||error|@|foundry.js:68260| ||_handleError|@|foundry.js:3468| ||(anonymous)|@|foundry.js:3450| ||value|@|socket.js:532| ||value|@|socket.js:459| ||L.emit|@|index.mjs:136| ||(anonymous)|@|manager.js:207| ||Promise.then (async)||| ||it|@|websocket-constructor.browser.js:5| ||value|@|manager.js:206| ||L.emit|@|index.mjs:136| ||value|@|index.js:131| ||value|@|manager.js:193| ||L.emit|@|index.mjs:136| ||value|@|socket.js:324| ||L.emit|@|index.mjs:136| ||value|@|transport.js:97| ||value|@|transport.js:89| ||ws.onmessage|@|websocket.js:69| ||Show less|

foundry.js:6629 TypeError: Cannot read properties of undefined (reading 'length')
at Preprocessor.advance (/data/application/re…processor.js:138:35)
at Tokenizer._consume (/data/application/re…zer/index.js:270:34)
at Tokenizer._runParsingLoop (/data/application/re…zer/index.js:221:29)
at Tokenizer.write (/data/application/re…zer/index.js:248:14)
at parseFragment (/data/application/re…dist/index.js:42:22)
at cleanHTML (/data/application/re…alidators.mjs:1:209)
at HTMLField.sanitizeHTMLField [as sanitize] (/data/application/re…tization.mjs:1:1235)
at Item._sanitizeFields (/data/application/re…document.mjs:1:7729)
at Item._sanitizeFields (/data/application/re…document.mjs:1:7956)
at Item.sanitizeUserInput (/data/application/re…document.mjs:1:7436)

|| || ||_onSubmit|@|foundry.js:6629| ||await in _onSubmit (async)||| ||_onSubmit|@|item-sheet.mjs:786| ||saveEditor|@|foundry.js:6773| ||onSave|@|item-sheet.mjs:410| ||_handleSave|@|prosemirror.js:19030| ||_onAction|@|prosemirror.js:19003| ||button.onclick|@|prosemirror.js:18504|



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GitHub
github.com › cvat-ai › cvat › issues › 5309
CVAT crashes when viewing Keypoint annotations · Issue #5309 · cvat-ai/cvat
November 17, 2022 - TypeError: Cannot read properties of undefined (reading 'addClass') at yw.activateShape (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784d9.min.js:2:5618087) at yw.activate (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784d9.min.js:2:5621272) at yw.notify (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784d9.min.js:2:5605174) at iy.notify (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784d9.min.js:2:5458777) at iy.activate (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784d9.min.js:2:5462895) at xw.activate (http://localhost:8080/assets/cvat-ui.33dd02fc10388e3784
Author: cvat-ai
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GitHub
github.com › cvat-ai › cvat › issues › 8086
can't access property "length", e is undefined · Issue #8086 · cvat-ai/cvat
June 26, 2024 - I used the SAM example and based my module on it - https://github.com/VeyDlin/cvat-clothing-segmentation. However, I continue to receive an error when trying to create the mask. Interaction error occurred can't access property "length", e is undefined
Author: cvat-ai
🌐
GitHub
github.com › cvat-ai › cvat › issues › 8896
CANNOT Upload Annotations · Issue #8896 · cvat-ai/cvat
January 2, 2025 - 4-Create a new task under the project 5-Drag .png files 6-Submit & Open to create the task 7- export annotations 8- run the object detection/models with the exported annotations from previous step>> this will create new annotations file (UpdatedAnnotations.xml) 9-import (UpdatedAnnotations.xml) to the same task in step 4 then receiving this error (Cannot read properties of undefined (reading 'push'))
Author: cvat-ai
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GitHub
github.com › microsoft › vscode › issues › 258611
Cannot read properties of undefined (reading 'length') · Issue #258611 · microsoft/vscode
July 29, 2025 - Type: Bug Cannot read properties of undefined (reading 'length') (at tsx element DA > EF > ise > oSe > Mo > > > sH > nSe > cSe > Sf) Extension version: 0.29.1 VS Code version: Code 1.102.3 (488a1f2, 2025-07-29T03:00:23.339Z) OS version: ...
Author: microsoft
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Reddit
reddit.com › r/learnjavascript › [deleted by user]
[deleted by user] : r/learnjavascript
July 15, 2022 - You’re getting this error when calling the length property on something. That means that something you have use .length on is undefined at some point.