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Comment by gmac | Hacker News Reader

I'm actually pretty fond of JavaScript, but here's a question that has caught me out in real code:

    const 
      x = [1, 10, 2],
      y = x.sort();

Now: what is the value of x? (Edit: and y?)

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Is the y relevant? Sort is in place and without a comparator function, it's going to convert the numbers to strings, so the array will remain the same.

If the question is about const, const with Arrays/Objects are by reference rather than value, nothing is stopping them from being modified later in the code.

In JavaScript every possible value has a .toString() representation* so it makes the most sense that the untyped/mixed array .sort() does lexicographic sorting. If you need numeric sort, use a TypedArray or provide an explicit arrow function.

* Except Object.create(null), which throws.

Yes, .sort((a, b) => b - a) is what I meant in this case.

I think perhaps this "makes the most sense" from a language designer/implementor's perspective, but it also gives ample opportunity for WTF moments in actual use.

I've been using JavaScript for around 15 years, and I've never used a comma to separate expressions. And I'd still go to MDN to look up if sort() is in place or not :p

The comma is not material here: the answer is the same if we write `const x = ...; const y = ...`.

And that's the first gotcha: sort() is in place.

Pretty sure I’ve actually tripped on sort() myself before by assuming it was a new array. It does make sense for performance though, creating a new array would be a bad default choice for performance, for the same reasons that forEach is generally faster than map all else being equal.

True. I like Ruby's solution with exclamation marks, such as `sort!`, to make this kind of behaviour obvious.

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