Axios Interceptors & Regional Time Zone Handling: Unresolved Decision on Date Serialization

Recommendation: Global ISO Serialization

To ensure consistency across regional time zones, you should implement a global request interceptor that recursively converts all Date instances into ISO 8601 strings. This prevents the loss of time-zone context and ensures that the server receives a standardized format regardless of the client's local settings.

Implementation Strategy

Because Axios uses JSON.stringify() internally, Date objects are typically converted to UTC strings. However, to maintain explicit control and handle nested structures, a recursive traversal is required.

1. Request Interceptor (Serialization)

Use a recursive function to walk the request payload. This ensures that Date objects nested within arrays or deep objects are caught without altering existing strings.

axios.interceptors.request.use((config) => {
  const serializeDates = (data) => {
    if (data instanceof Date) return data.toISOString();
    if (Array.isArray(data)) return data.map(serializeDates);
    if (data !== null && typeof data === 'object') {
      return Object.fromEntries(
        Object.entries(data).map(([key, value]) => [key, serializeDates(value)])
      );
    }
    return data;
  };

  if (config.data) {
    config.data = serializeDates(config.data);
  }
  return config;
});

2. Response Interceptor (Deserialization)

A complementary response interceptor is recommended to restore Date objects. This allows the application logic to use date methods (like .getTime()) immediately without manual parsing in every component.

• Detection: Use a strict RFC3339/ISO 8601 regex to identify date strings.
• Ambiguity: If a string matches the pattern but lacks an offset (no 'Z' or '+/-HH:mm'), treat it as a plain string to avoid incorrect UTC assumptions.

Technical Assumptions and Risks

Factor	Assumption/Risk	Mitigation
Performance	Deep traversal may slow down massive payloads.	Limit recursion depth or target specific keys if payloads exceed several MBs.
Data Integrity	Some strings may accidentally match the ISO regex.	Use a highly specific regex that requires the full ISO format.
Version	Assumes Axios 1.x+ and modern JS environments.	Verify Object.fromEntries support in target browsers.

Verification Steps

1. Round-trip Test: Send a nested object containing a Date, receive it back, and verify the final object is an instance of Date with the same millisecond value.
2. Negative Test: Send a string that looks like a date but is intentionally a string; verify the response interceptor does not convert it.

Diagnostic Question: Does your API contract require the preservation of the local time-zone offset (e.g., +05:30) rather than converting everything to UTC (Z)? If so, .toISOString() is insufficient, and a library like date-fns or Luxon must be used in the interceptor.