[lomnakkus]

The JS way is a mistake, intentional or not.

Here's a little thought experiment: Your program ends up with an "undefined" in some variable 'x'. How did that happen? In JS it can happen in any number of weird and wonderful ways, e.g. you called a function which did a 'v[i]' or it could have just fallen off the end because someone forgot to check a return path, or...

In Python there's much less scope what the problem could be. Since v[i] will just throw an IndexError, you know that the problem couldn't possibly be stray index or similar.

That is a much better experience for finding problems in one's code.

[millstone]

But JS programs must execute in uncontrolled environments, e.g. browser engines from the past and future with random extensions installed. A bondage-and-discipline language may help developers find logic bugs, but will make the users' experiences worse.

[lomnakkus]

How is "there was a JavaScript error on this page" informational icon any worse than an order total of "undefined" or that the page just doesn't seem to be reacting to clicks? I'd argue that the former is much better UX -- at least the user isn't confused whether it's them that's doing something wrong or it's the page that just shoddily implemented.

[codetrotter]

> at least the user isn't confused whether it's them that's doing something wrong or it's the page that just shoddily implemented

Users generally ignore all messages coming from their computers. They routinely blame their computers for doing things that the computers are not doing at all. Like, oh I can’t find the document I wrote three weeks ago -> obviously my computer is being disobedient.

Anyway, I don’t blame the users. To them the computer is entirely uninteresting and they don’t want to care about the sorts of concerns that we technically minded people do.

A broken page is a broken page and it doesn’t matter to the user why the page is broken. The only thing that matters to them is, can they do the thing they wanted to do or not. And like the sibling said, the web browsers are surprisingly good at handling broken code.

[lomnakkus]

Did you read what I said at all?

"Order total: undefined" is hugely different from "There was an error -- maybe just leave the page, yeah?".

[millstone]

Banker vs moon rover. B&D languages panic at the first whiff of deviation between the compile-time and runtime environments. But I loaded cnn.com, and my third-party ad blocker did god-knows-what to dozens of requests, with a bazillion unexpected undefineds, and yet the page still rendered.

The web powers through!

[lomnakkus]

This has nothing to do with undefined vs. exceptions, sorry. You can do example the same with a powerful enough sandbox -- e.g. what WebAsm does to avoid hostile code taking over your computer.

It has everything to do with sandboxing (or not). Ads being served by third parties should not be able to influence the JS running in the page.