Improve Uncaught Errors

[kuceb]

on Uncaught Errors

• if there is no err.stack, e.g syntax error, construct a better error
• if there is a stack, cut out the cypress related lines

[mackelito]

Guess this is the same issue I have... causes tests to fail.

cypress_runner.js:65225 Uncaught TypeError: Cannot read property 'replace' of undefined
    at Object.appendErrMsg (cypress_runner.js:65225)
    at Object.createUncaughtException (cypress_runner.js:58408)
    at Object.onUncaughtException (cypress_runner.js:61281)
    at onError (cypress_runner.js:60780)

[benjie]

I've just spent an hour getting to know Cypress intimately to track down the error I was getting. Spoiler: turns out the error was that electron doesn't currently support optional catch binding in try block:

try {
  ...
} catch {
  ...
}

The error I was receiving was:

Uncaught SyntaxError: Unexpected token {

This error originated from your application code, not from Cypress.

When Cypress detects uncaught errors originating from your application it will automatically fail the current test.

This behavior is configurable, and you can choose to turn this off by listening to the 'uncaught:exception' event.

https://on.cypress.io/uncaught-exception-from-application

This doesn't contain anything useful for tracking down what is causing the error since there's {s everywhere.

After much exploration through the devtools I landed here:

This gave me the information I needed - the file, line number and column number of the syntax error. From then it only took a few more seconds to track down the actual syntax incompatibility.

The issue here seems to be that the source, lineno and colno information are being explicitly dropped here:

cypress/packages/driver/src/cy/errors.coffee

Lines 29 to 30 in 55b352a

	createUncaughtException = (type, args) ->
	[msg, source, lineno, colno, err] = args

cypress/packages/driver/src/cy/errors.coffee

Lines 39 to 44 in 55b352a

	createErrFromMsg = ->
	new Error $utils.errMessageByPath("uncaught.error", { msg, source, lineno })
	## if we have the 5th argument it means we're in a super
	## modern browser making this super simple to work with.
	err ?= createErrFromMsg()

Because the error (argument 5) exists, the other details are discarded, which leads to a less-than-optimal debugging experience.

As far as I can tell, there's no way for me to extract these details with any cypress hooks, for example by the time it hits the uncaught:exception hook these details have been dropped (I think?).

Suggestion: add source, lineno and colno to the error object and ensure they're in the error message.

[cypress-bot]

The code for this is done in cypress-io/cypress#3930, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[cypress-bot]

Released in 4.6.0.

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