The TrackJS Blog

Debugging Articles

Debugging: "Cannot read property 'length' of undefined."

Debugging: "Cannot read property 'length' of undefined."

By Todd H Gardner

While looking into an issue with Microsoft Edge and the Facebook sdk a few weeks ago, we ran into a very common error: Cannot read property ‘length’ of undefined. In fact, this is the 6th most common error, affecting nearly 28% of accounts.

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Debugging: "Failed to construct 'Request': Invalid Argument." in Edge

Debugging: "Failed to construct 'Request': Invalid Argument." in Edge

By Todd H Gardner

Nothing changed in your code. All of a sudden, a tidal wave of errors start happening for Microsoft Edge users. What the heck happened? On August 28th, 2019, many TrackJS customers saw a sudden surge in errors from Microsoft Edge browsers: Failed to construct 'Request': Invalid Argument and Fail...

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Debugging: "Refused to get unsafe header" in Chrome

Debugging: "Refused to get unsafe header" in Chrome

By Todd H Gardner

Recently, we ran into a scary looking error message in the Chrome console, Refused to get unsafe header "TrackJS-Correlation-Id". Our code was indeed trying to read this header from a request, so we explored this right away. The funny thing is, other than the error message in Chrome, everything w...

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Debugging: Cannot read property 'Id' of undefined

Debugging: Cannot read property 'Id' of undefined

By Eric Brandes

We understand the value of JavaScript error monitoring here at TrackJS. Consequently, we run TrackJS on all of our own web properties to log our JS errors. We’re dilligent about fixing errors as they happen, and most issues are caught in development environments, or immediately in production. Ho...

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Debugged: Debugging Empty String

Debugged: Debugging Empty String

By Todd H Gardner

Empty String. An infuriatingly vague error message that leaves few clues about what’s going wrong. A customer recently experienced a lot of these, and asked for our help debugging it. This is that story.

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Common Redux Bugs

Common Redux Bugs

By Todd H Gardner

Redux is an amazing JavaScript library that has become mainstream because of its simplicity, tiny 2kb size, and excellent documentation. Redux assists developers to manage state in JavaScript applications and ensure it performs consistently, regardless of the environment. However, despite Redux’...

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Debugged: Internet Explorer 11 Crash on JSON.stringify

Debugged: Internet Explorer 11 Crash on JSON.stringify

By Todd H Gardner

Internet Explorer 11 crashes when JSON.stringify is called on an HTMLFormElement that contains duplicate named inputs. This is particularly concerning because radio inputs will certainly have duplicate names.

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Debugging JavaScript in Production

Debugging JavaScript in Production

By Todd H Gardner

The web is a hostile place and our JavaScript apps will inevitably break. Browser changes, invasive plugins, unstable networks, or just plain bugs—something is going to go wrong. When it does, we need to be ready. We need to know what went wrong and how to fix it or our users just won’t come back.

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When Form.Submit is not a Function

When Form.Submit is not a Function

By Todd H Gardner

The HTMLFormElement is weird. Although it was designed to make working with forms easier in the early days of the web, there are many subtle problems and inconsistencies that create nasty JavaScript bugs.

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Debugged: "nsresult: 0x805e0006" on Firefox

Debugged: "nsresult: 0x805e0006" on Firefox

By Todd H Gardner

In Mozilla Firefox, a request to load an external origin was attempted and externally blocked. The request could have been canceled by a browser extension, such as an adblocker or antivirus, or because the remote origin did not return a proper CORS response.

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Debugged: "Attempted to assign to readonly property." iOS 8 TypeError

Debugged: "Attempted to assign to readonly property." iOS 8 TypeError

By Todd H Gardner

A webkit bug that shipped in iOS 8 beta 5 and appears to have been partially included in the launch of iOS 8 and 8.1 is affecting many of our customers. It does not seem to impact all iOS8 uniformly; different versions of webkit seem to be involved.

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