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fix: strip field prefix before erroring on duplicates #16151

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Merged
Rich-Harris merged 1 commit into from
Jun 24, 2026
Merged

fix: strip field prefix before erroring on duplicates #16151

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5 changes: 5 additions & 0 deletions .changeset/happy-parts-search.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
'@sveltejs/kit': patch
---

fix: strip field prefix before erroring on duplicates
8 changes: 4 additions & 4 deletions packages/kit/src/runtime/form-utils.js
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Original file line number Diff line number Diff line change
Expand Up @@ -42,10 +42,6 @@ export function convert_formdata(data) {

if (is_array) key = key.slice(0, -2);

if (values.length > 1 && !is_array) {
throw new Error(`Form cannot contain duplicated keys — "${key}" has ${values.length} values`);
}

// an empty `<input type="file">` will submit a non-existent file, bizarrely
values = values.filter(
(entry) => typeof entry === 'string' || entry.name !== '' || entry.size > 0
Expand All @@ -60,6 +56,10 @@ export function convert_formdata(data) {
values = values.map((v) => v === 'on');
}

if (values.length > 1 && !is_array) {
throw new Error(`Form cannot contain duplicated keys — "${key}" has ${values.length} values`);
}

set_nested_value(result, key, is_array ? values : values[0]);
}

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