Summary

Fixes an issue in formDataToJSON where multiple entries with the same key result in nested arrays instead of a flat array.

Problem

When a FormData object contains more than two entries with the same key:

formData.append('file', 'A');
formData.append('file', 'B');
formData.append('file', 'C');

The current implementation produces:
[[A, B], C]

Instead of the expected:
[A, B, C]

Fix

Ensure that values are appended to an existing array instead of wrapping repeatedly:

if (utils.hasOwnProp(target, name)) {
if (utils.isArray(target[name])) {
target[name].push(value);
} else {
target[name] = [target[name], value];
}
}

Impact

• Produces consistent flat arrays
• Prevents unexpected nested structures
• Improves handling of repeated FormData keys

Verification

Tested locally by appending multiple values with the same key and confirming output is a flat array.

Summary by cubic

Fixes formDataToJSON so repeated FormData keys produce a flat array (e.g., [A, B, C]) instead of nested arrays. Improves consistency with common FormData semantics.

Description

Ensures duplicate keys append to an existing array, rather than wrapping multiple times.

• Summary of changes
  • In lib/helpers/formDataToJSON.js, push to target[name] if it’s already an array; otherwise wrap once as [existing, value].
• Reasoning
  • Previous logic nested arrays after the second duplicate (e.g., [[A, B], C]). The new logic returns a flat array for all duplicates.
• Additional context
  • package-lock.json updated (peer flags and minor cleanup). No runtime impact.

Docs

• Update formDataToJSON docs to clarify: repeated keys return a flat array in insertion order.
• Add a brief note for users migrating from earlier v1.x that nested arrays are no longer produced.

Testing

• No tests added in this PR.
• Tests recommended:
  • 3+ duplicates: A, B, C → [A, B, C]
  • 2 duplicates: A, B → [A, B]
  • Single value remains scalar (A) and becomes array only on second insert
  • Mixed value types (e.g., File, Blob, string) with duplicates remain flat and ordered.

^{Written for commit 1c33ad5. Summary will update on new commits.}