AJAX Error Handling

AJAX Error Handling: free step-by-step lesson with examples, common mistakes, and interview tips — part of jQuery Tutorial on Toolliyo Academy.

8 min read Updated 8/23/2026

On this page

jQuery Tutorial · Lesson 46 of 100

AJAX Error Handling

Setup & DOM ✓ → Events Effects AJAX → Perf & Integrate → Ship & Projects

Events Effects AJAX · 2 — Interact · ~6 min · AJAX and APIs

What is this?

Failures include network errors, HTTP 4xx/5xx, timeouts, and parsererrors. .fail(xhr, status, error) distinguishes them so QueryVerse can show useful messages.

Why should you care?

Silent failures make ops teams distrust the UI — always surface something actionable.

See it live — copy this example

Examples include the jQuery 3.7 CDN. Paste into an HTML file or use Run Example to preview.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>QueryVerse</title>
  <style>
    body { font-family: system-ui, sans-serif; margin: 1.25rem; }
    .box { padding: .75rem; border: 1px solid #ccc; border-radius: 8px; margin: .5rem 0; }
    .muted { color: #666; }
    button { margin-right: .35rem; margin-top: .35rem; }
    input, select, textarea { margin: .25rem 0; }
    table { border-collapse: collapse; width: 100%; }
    th, td { border: 1px solid #ddd; padding: .4rem .55rem; text-align: left; }
    .hidden { display: none; }
    .row-odd { background: #f7f7f7; }
    .active { font-weight: 700; }
    .toast { background: #111; color: #fff; padding: .5rem .75rem; border-radius: 6px; }
  </style>
</head>
<body>
  <button type="button" id="ok">Good URL</button>
  <button type="button" id="bad">404 URL</button>
  <pre id="out" class="box muted"></pre>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  function explain(xhr, status, err) {
    return JSON.stringify({ status: status, http: xhr.status, err: String(err) }, null, 2);
  }
  $('#ok').on('click', function () {
    $.getJSON('https://jsonplaceholder.typicode.com/posts/1')
      .done(function (p) { $('#out').text('OK: ' + p.title); })
      .fail(function (x, s, e) { $('#out').text(explain(x, s, e)); });
  });
  $('#bad').on('click', function () {
    $.getJSON('https://jsonplaceholder.typicode.com/posts/999999')
      .done(function () { $('#out').text('unexpected'); })
      .fail(function (x, s, e) { $('#out').text(explain(x, s, e)); });
  });
});
</script>
</body>
</html>

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>QueryVerse</title>
  <style>
    body { font-family: system-ui, sans-serif; margin: 1.25rem; }
    .box { padding: .75rem; border: 1px solid #ccc; border-radius: 8px; margin: .5rem 0; }
    .muted { color: #666; }
    button { margin-right: .35rem; margin-top: .35rem; }
    input, select, textarea { margin: .25rem 0; }
    table { border-collapse: collapse; width: 100%; }
    th, td { border: 1px solid #ddd; padding: .4rem .55rem; text-align: left; }
    .hidden { display: none; }
    .row-odd { background: #f7f7f7; }
    .active { font-weight: 700; }
    .toast { background: #111; color: #fff; padding: .5rem .75rem; border-radius: 6px; }
  </style>
</head>
<body>
  <button type="button" id="ok">Good URL</button>
  <button type="button" id="bad">404 URL</button>
  <pre id="out" class="box muted"></pre>
<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
$(function () {
  function explain(xhr, status, err) {
    return JSON.stringify({ status: status, http: xhr.status, err: String(err) }, null, 2);
  }
  $('#ok').on('click', function () {
    $.getJSON('https://jsonplaceholder.typicode.com/posts/1')
      .done(function (p) { $('#out').text('OK: ' + p.title); })
      .fail(function (x, s, e) { $('#out').text(explain(x, s, e)); });
  });
  $('#bad').on('click', function () {
    $.getJSON('https://jsonplaceholder.typicode.com/posts/999999')
      .done(function () { $('#out').text('unexpected'); })
      .fail(function (x, s, e) { $('#out').text(explain(x, s, e)); });
  });
});
</script>
</body>
</html>

Result