feat: add ECONNREFUSED error code constant to AxiosError (#10680)

Adds `AxiosError.ECONNREFUSED` as a typed constant alongside existing
error codes like ECONNABORTED and ETIMEDOUT, enabling type-safe error
code checks without hardcoding strings.

Closes #6485

Co-authored-by: marcosnocetti <marcos.nocetti@ubots.com.br>
Co-authored-by: Jay <jasonsaayman@gmail.com>

index.d.cts

@@ -162,6 +162,7 @@ declare class AxiosError<T = unknown, D = any> extends Error {
   static readonly ERR_CANCELED = 'ERR_CANCELED';
   static readonly ERR_FORM_DATA_DEPTH_EXCEEDED = 'ERR_FORM_DATA_DEPTH_EXCEEDED';
   static readonly ECONNABORTED = 'ECONNABORTED';
+  static readonly ECONNREFUSED = 'ECONNREFUSED';
   static readonly ETIMEDOUT = 'ETIMEDOUT';
 }
 

index.d.ts

@@ -519,6 +519,7 @@ export class AxiosError<T = unknown, D = any> extends Error {
   static readonly ERR_CANCELED = 'ERR_CANCELED';
   static readonly ERR_FORM_DATA_DEPTH_EXCEEDED = 'ERR_FORM_DATA_DEPTH_EXCEEDED';
   static readonly ECONNABORTED = 'ECONNABORTED';
+  static readonly ECONNREFUSED = 'ECONNREFUSED';
   static readonly ETIMEDOUT = 'ETIMEDOUT';
 }
 

lib/core/AxiosError.js

@@ -78,6 +78,7 @@ AxiosError.ERR_BAD_OPTION_VALUE = 'ERR_BAD_OPTION_VALUE';
 AxiosError.ERR_BAD_OPTION = 'ERR_BAD_OPTION';
 AxiosError.ECONNABORTED = 'ECONNABORTED';
 AxiosError.ETIMEDOUT = 'ETIMEDOUT';
+AxiosError.ECONNREFUSED = 'ECONNREFUSED';
 AxiosError.ERR_NETWORK = 'ERR_NETWORK';
 AxiosError.ERR_FR_TOO_MANY_REDIRECTS = 'ERR_FR_TOO_MANY_REDIRECTS';
 AxiosError.ERR_DEPRECATED = 'ERR_DEPRECATED';