Use Object.create(null) instead of {} to compute keyed diffs #180
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`{}` creates an empty object but which still contains methods and
properties like `toString`. Checking `changes[key]` when the key is
for instance `toString` creates false positives in that check.
In practice, the algorithms in `_VirtualDom_insertNode` and `_VirtualDom_removeNode`
end up with the correct behavior because they recurse with a modified
key, but do so with an unnecessary iteration.
`Object.create(null)` create an empty object without any methods or
properties, leading to no false positives.
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Why not |
Author
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Because Elm currently compiles down to ES5, where Map is not available. |
ahankinson
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Nov 20, 2025
fixes elm#187 fixes elm#182 fixes elm/html#44 fixes elm/browser#121 fixes elm/browser#66 fixes elm#62 fixes elm#127 fixes elm#147 fixes elm#159 fixes elm#105 fixes elm#162 fixes elm#171 fixes elm#175 fixes elm#178 fixes elm#180 fixes elm#183 fixes elm#189 fixes elm#166 fixes elm/html#160 fixes elm/html#177 fixes elm/compiler#2069
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This is a minor improvement pull request.
{}creates an empty object but which still contains methods and properties liketoString. Checkingchanges[key]when the key is for instancetoStringcreates false positives in that check.I was looking whether into whether this caused bugs, but in practice, the algorithms in
_VirtualDom_insertNodeand_VirtualDom_removeNodeend up with the correct behavior because they recurse with a modified key, but do so with an unnecessary iteration.Object.create(null)creates an empty object without any methods or properties, leading to no false positives and one less unnecessary iteration.