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Inclusive slice operation with string end gives wrong result #882

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alangpierce opened this Issue Feb 27, 2017 · 0 comments

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alangpierce commented Feb 27, 2017

decaffeinate is producing the wrong JavaScript based on my CoffeeScript input:

a = [1, 2, 3, 4, 5]
start = '1'
end = '3'
console.log a[start..end]

(repl)

I get this output:

a = [1, 2, 3, 4, 5];
start = '1';
end = '3';
console.log(a.slice(start, end + 1 || undefined));

Here's what I expect it to be instead:

a = [1, 2, 3, 4, 5];
start = '1';
end = '3';
console.log(a.slice(start, +end + 1 || undefined));

Otherwise, it takes the range from '1' to '31'.

@alangpierce alangpierce self-assigned this Feb 27, 2017

alangpierce added a commit to alangpierce/decaffeinate that referenced this issue Mar 7, 2017

fix: ensure that inclusive slice bounds are numbers
Fixes decaffeinate#882

We need to put a `+` unary op at the front to avoid string concatenation when
adding `1`.

alangpierce added a commit that referenced this issue Mar 7, 2017

fix: ensure that inclusive slice bounds are numbers (#905)
Fixes #882

We need to put a `+` unary op at the front to avoid string concatenation when
adding `1`. Also add a space after the `+` when it would otherwise create `++`.
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