Better Errors in JS
undefined is not a function
How to collect error messages
Any way you run JS can be a good way to get an error message: in a web browser, in Node.js, etc. Errors that you file issues on should be reduced to a minimal test case (ideally just a couple lines when possible). To file an issue, you should understand what went wrong in the program, and what JS is trying to tell you went wrong (even if the message itself doesn't indicate things clearly).
You can use eshost and jsvu to run a JS code snippet across many JS engines. These projects make it easy to run a snippet across several engines. Sometimes, one of them will have a good message, which could be used as a model for the others.
The goal of this project is to be a resource to JS engine developers, providing them with a ready-made wishlist of error conditions and messages, so that they can focus on on the implementation.
This project is focused on error messages from the JS engine itself. These messages are all of the six native error types in the JS standard:
SyntaxError. (Other error types are generated by other pieces of software, so if you file an issue about them, it's less likely to get through to the right people who can fix it.)