Query Params With Arrays

[HamishBuckmaster]

Query params with arrays are stringified into a single comma-separated value instead of repeated keys

• Library: better-fetch
• Version: latest (1.1.18)
• Environment: [Node/Browser], [runtime version], [OS]

Summary

When passing an array as a query parameter, better-fetch stringifies the array into a single comma-separated value rather than encoding repeated keys.

Example

• Input code (simplified):

betterFetch('/path', {
  query: { status: ['active', 'paused'] },
});

• Actual request:

/path?status=active,paused

Sometimes it even wraps in quotes depending on how it’s constructed:

/path?status='active,paused'

• Expected request:

/path?status=active&status=paused

Why this matters

• Many backends (including common frameworks and API gateways) expect arrays to be represented by repeated keys.
• The current behavior can lead to incorrect filtering/parsing on the server side unless the server specifically supports comma-separated lists.

Desired behavior/options

• Encode arrays as repeated keys by default: key=value1&key=value2
• Optionally support configurable array formats, e.g.:
  • repeated: key=a&key=b (default)
  • comma: key=a,b
  • indices: key[0]=a&key[1]=b
  • brackets: key[]=a&key[]=b
• Do not add quotes around values.

Workarounds tried

• Manually building the query string with URLSearchParams:

const qs = new URLSearchParams();
['active', 'paused'].forEach((s) => qs.append('status', s));
betterFetch(`/path?${qs.toString()}`, {
  // ...
});

This works, but defeats the convenience of the built-in query option.

Steps to reproduce

1. Use better-fetch with a query option containing an array value:

betterFetch('/path', { query: { status: ['active', 'paused'] } });

2. Observe the resulting URL/request being made.

Expected

/path?status=active&status=paused

Actual

/path?status=active,paused