javascript 42 lines · 8 steps

A resilient fetch wrapper with retries and timeout

How to merge default request options and wrap fetch with retry and abort-based timeout logic.

Explained by highlit
Intermediate fetch retry timeout abortcontroller config-merging
1const DEFAULT_OPTIONS = {
2 method: 'GET',
3 timeout: 5000,
4 retries: 3,
5 headers: {
6 Accept: 'application/json',
7 'Content-Type': 'application/json',
8 },
9 cache: 'no-store',
10};
11 
12function resolveRequestOptions(overrides = {}) {
13 const { headers: overrideHeaders, ...restOverrides } = overrides;
14 
15 return {
16 ...DEFAULT_OPTIONS,
17 ...restOverrides,
18 headers: {
19 ...DEFAULT_OPTIONS.headers,
20 ...overrideHeaders,
21 },
22 };
23}
24 
25export async function apiFetch(url, overrides) {
26 const { timeout, retries, ...fetchOptions } = resolveRequestOptions(overrides);
27 
28 for (let attempt = 0; attempt <= retries; attempt++) {
29 const controller = new AbortController();
30 const timer = setTimeout(() => controller.abort(), timeout);
31 
32 try {
33 const response = await fetch(url, { ...fetchOptions, signal: controller.signal });
34 if (!response.ok && attempt < retries) continue;
35 return response;
36 } catch (err) {
37 if (attempt === retries) throw err;
38 } finally {
39 clearTimeout(timer);
40 }
41 }
42}
01 / 01
STEP 01

Walkthrough

Space play ←→ step click any line
Three takeaways
  1. 1Nested config objects need a deep merge so overriding one header doesn't wipe the rest.
  2. 2AbortController plus setTimeout gives fetch the request timeout it lacks natively.
  3. 3A retry loop must distinguish the final attempt so it can surface the real error instead of swallowing it.

Related explainers

javascript 
function evaluate(expression) {
  const tokens = tokenize(expression);
  let pos = 0;
 

Building a recursive descent calculator

parsing recursion operator-precedence
Intermediate 8 steps
javascript 
import { useState, useEffect, useCallback, useRef } from 'react';
 
const cache = new Map();
const inflight = new Map();

Building a stale-while-revalidate hook in React

caching request-deduplication custom-hooks
Advanced 10 steps
javascript 
import { useEffect, useRef, useState } from 'react';
 
export function useDelayedFlag(active, delay = 300) {
  const [visible, setVisible] = useState(false);

Delaying a loading spinner with a React hook

custom-hooks debouncing cleanup
Intermediate 8 steps
javascript 
const SWIPE_THRESHOLD = 80;
const MAX_TRANSLATE = 120;
 
export function attachSwipeToDismiss(element, onDismiss) {

Building a swipe-to-dismiss gesture in JS

touch-events gesture-detection dom-manipulation
Intermediate 10 steps
javascript 
const { pool } = require('./db');
 
function withTransaction() {
  return async (req, res, next) => {

A per-request transaction middleware in Express

middleware database-transactions connection-pooling
Advanced 7 steps
javascript 
function collapseConsecutiveLogs(lines, { keyFn = (l) => l.message } = {}) {
  const groups = [];
 
  for (const line of lines) {

Collapsing consecutive log lines in JavaScript

grouping run-length-encoding data-transformation
Intermediate 7 steps

Share this explainer

Here's the card — post it anywhere.

A resilient fetch wrapper with retries and timeout — share card
Made with highlit — turn any snippet into a walkthrough like this in about a minute.
Explain your code