Debugging JavaScript Errors
Dive into specific errors with examples, explanations, and debugging tips.
Failed to fetch
Network errors happen, and the Fetch API has certain ways of telling you that. One of them is the uninspiring error message Failed to fetch.
ResizeObserver loop completed with undelivered notifications.
The error, ResizeObserver loop completed with undelivered notifications. is a surprisingly common message that many TrackJS customers capture from their site...
Object Not Found Matching Id:1, MethodName:update, ParamCount:4
Starting in April of 2024, lots of websites that use TrackJS (as well as other vendors) started getting large volumes of this error:, Object Not Found Matchi...
Cannot read properties of undefined (reading 'id')
We’ll often run into errors like “Cannot read properties of undefined (reading ‘id’)”. It’s one of the most common errors that developers encounter during we...
Cannot read properties of undefined (reading 'length')
One of the most common errors we record, “Cannot read properties of undefined (reading ‘length’)”, turned up in our own logs recently while looking into an i...
Refused to get unsafe header
We ran into a scary looking error message in the Chrome console, Refused to get unsafe header "TrackJS-Correlation-Id". Our code was trying to read this head...
form.submit is not a function
HTML Forms have some really strange JavaScript behavior. We’ll often want to add JavaScript to enhance form controls and actions, but sometimes weird things ...
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The easiest way to track JavaScript errors. TrackJS monitors real errors from your website and reports all the context you need to recreate the problem and fix the bug. No complicated dashboards or custom queries, just the data you need to build better web applications.