fix: preserve configuration for custom instance

Fixes JustinBeckwith#68.

src/index.ts

@@ -90,7 +90,10 @@ export type RaxConfig = {
  */
 export function attach(instance?: AxiosInstance) {
 	instance = instance || axios;
-	return instance.interceptors.response.use(onFulfilled, onError);
+	return instance.interceptors.response.use(
+		onFulfilled,
+		async (error: AxiosError) => onError(instance!, error),
+	);
 }
 
 /**
@@ -165,7 +168,7 @@ function parseRetryAfter(header: string): number | undefined {
 	return undefined;
 }
 
-async function onError(error: AxiosError) {
+async function onError(instance: AxiosInstance, error: AxiosError) {
 	if (isCancel(error)) {
 		throw error;
 	}
@@ -175,7 +178,7 @@ async function onError(error: AxiosError) {
 	config.retry = typeof config.retry === 'number' ? config.retry : 3;
 	config.retryDelay =
 		typeof config.retryDelay === 'number' ? config.retryDelay : 100;
-	config.instance = config.instance || axios;
+	config.instance = config.instance || instance;
 	config.backoffType = config.backoffType || 'exponential';
 	config.httpMethodsToRetry = normalizeArray(config.httpMethodsToRetry) || [
 		'GET',

test/index.ts

@@ -111,6 +111,22 @@ describe('retry-axios', () => {
 		}
 	});
 
+	it('should retry at least the configured number of times for custom client', async function () {
+		this.timeout(10_000);
+		const scopes = [
+			nock(url).get('/').times(3).reply(500),
+			nock(url).get('/').reply(200, 'milk'),
+		];
+		const client = axios.create();
+		interceptorId = rax.attach(client);
+		const cfg: rax.RaxConfig = {url, raxConfig: {retry: 4}};
+		const result = await client(cfg);
+		assert.strictEqual(result.data, 'milk');
+		for (const s of scopes) {
+			s.done();
+		}
+	});
+
 	it('should not retry more than configured', async () => {
 		const scope = nock(url).get('/').twice().reply(500);
 		interceptorId = rax.attach();