Earlier quoted context omitted.
alert()
Which didn't help much when there was a syntax error somewhere close by causing the browser to silently terminate parsing/executing the code. At least these days the browsers tend to dump error messages into the console when this happens... In theory that could have been caught by a good jslint/syntax checker but those were a few years in the future too. Early, JS development really sucked, its only slightly better t…
I recall a dramatic bug where, in 2012, I rolled out a new version of a web GUI with some JS mixed in it to an intranet audience of IE 7 and Firefox users. It initially looked good, but then reports came in that IE users couldn't use one of the buttons. After much debugging and confusion, it turned out that there was a trailing comma at the end of an array literal (i.e. `[1,2,3,]` instead of `[1,2,3]`). Firefox accepted that, but IE 7 didn't. (I think IE 8 added support for trailing commas.)