> [1, 2, 3] + [4, 5, 6] // -> "1,2,34,5,6"
What would you expect instead?
> [,,,].length // -> 3
Is there any use case where you would want to deal with sparse arrays?
An addition operation over two numerical vectors of length 3.
I would expect the result to match its inputs and provide a numerical vector of length 3.
Thus: [5, 7, 9]
So if applying an operator to arrays spread the operation across all the elements that way, it would imply that the same should happen generally for all object properties, with whatever weird implications that would entail.
a.foo = 1
b.foo = 'there'
a + b // { foo: '1there' } ?> What would you expect instead?
If I let my first instinct speak:
[1,2,3,4,5,6]
And then if I think a little more, then maybe:
[5,7,9] //with obvious caveats
In no way do I expect what GP actually provided.
[1] https://tc39.es/ecma262/multipage/ecmascript-language-expres...
I am very happy with JS and TS and I think the coercion rules are easily worked around with linter rules and policies, but they are definitely weird and I think the language would be better if it simply threw exceptions instead. But then, such an issue shoud not be surprising for a language that was designed in 10 days.
If someone does not like the ECMAScript specification, that is fine. But at least use a proper unofficial documentation like MDN.
If you ask experts it is because you want to get an actual correct answer, but if you ask neophytes it is because you want to get an answer that might be obvious even if not correct.
Not really. Now explain why [,,,].map((e,i) => i) is [,,,] instead of [1,2,3] please ;)
Array(4) // [empty × 4]
a=[]; a.length=4; a // [empty × 4]
Array(4).map(n => n) // [empty × 4]
[,,1,,].map(n => n) // [empty × 2, 1, empty]
Array.from(Array(4)).map((n,i) => i) // [0, 1, 2, 3]
Array(4).fill(1) // [1, 1, 1, 1]