[b0rsuk]

Few people do that outside of code obfuscation contests, but the point is JS has heaps of gotchas like that, each waiting to bite you. How about:

x = 5;

(no var declaration). Extremely easy to do by accident. Lots of these will be left for backwards compatibility. In JS errors often go silent and I developed a strong dislike for any language that does that, including Vimscript and Lua (and I do like Vim).

[nobleach]

I'd agree that global declaration is far more egregious. A sibling comment recommends a linter, and I'd probably agree. It's sad that it was ever allowed as one that is copying and pasting code to another location can easily cause this case to happen.

[jimws]

Problems like this can be easily caught by linters like eslint or standardjs.

[s_y_n_t_a_x]

No JS developer would do that.

We all know that is global.

Nowadays you use `const` or `let`.

Any JS developer will have a linter that will tell them incase they somehow made that mistake.

[tombert]

Eh, I actually like JS but I have definitely forgotten to add a "var" or "let" a few times, or sometimes I will do it correctly, get a bit overzealous with cutting, and accidentally remove the initial var declaration.

I'm not saying that it breaks the language, but it definitely is irritating, especially if you're not using a linter.

[s_y_n_t_a_x]

I come from Lua so I'm used to declaring local variables with "local".

Also, I like knowing which variables won't be reassigned (const), and which will (let).

[shakna]

Whilst I do find it irritating, I don't mind about the scope default so much, but I've certainly run into it (forgetting to specify) a lot.

Mostly because JS is not the only language that I'll be working with at a time, and if I'm dancing between three or four and they have similar syntax, then mistakes creep in.

[jdminhbg]

That's all fine, but those are all workarounds for a design mistake in the language.

[s_y_n_t_a_x]

No it's a choice, apparently people can't have one.