jQuery jQuery.support Property

What You’ll Learn

The jQuery.support object stores internal browser capability test results that jQuery uses when normalizing DOM and CSS behavior. This tutorial explains what it is, why it was deprecated in 1.9, what changed in 1.11+, and what to use instead when you need real feature detection in your own code.

Introduction

Early web development required dozens of tiny browser-specific workarounds. jQuery centralised those checks in one place: the jQuery.support object. When you called $.css(), $.ajax(), or $.clone(), jQuery consulted support flags to decide which code path was safe on the current browser.

That design helped jQuery maintain one consistent API across IE, Firefox, Safari, and Opera. However, exposing those flags encouraged plugins and application code to depend on undocumented property names. When browsers fixed old bugs, jQuery removed obsolete flags — and external code broke.

Since jQuery 1.9, the official documentation marks jQuery.support as deprecated for external use. You should treat it as read-only curiosity when debugging legacy projects, not as a feature-detection toolkit for new features.

Understanding the jQuery.support Property

jQuery.support is a plain JavaScript object attached to the global jQuery namespace. Each property name describes a browser quirk or capability — historically things like whether the CSS opacity property worked reliably, whether <tbody> elements were auto-inserted in tables, or whether cloned nodes preserved event handlers.

The object is populated when jQuery loads (or lazily when a module first needs a test). Values are typically booleans, though since jQuery 1.11 some entries are functions that run the test on first call and cache the result. That keeps unused tests from slowing initial page load.

📝 Syntax

Access the global support object — there are no parameters:

jQuery.support
// or
$.support

Return value

• An Object whose properties represent internal feature-test results.
• Property names and meanings are not guaranteed — they change as jQuery internals evolve.
• Since jQuery 1.11+, the object is not reliably JSON.stringify-able because some values are functions.

Read-only inspection pattern

// Educational only — do not branch app logic on these keys
console.log(typeof $.support);           // "object"
console.log(Object.keys($.support));     // current internal flags in this jQuery version

Examples Gallery

These examples inspect jQuery.support for learning — they do not recommend using it in production logic. Open DevTools or use the Try-it links with jQuery 3.7.1.

console.log("jQuery version:", $.fn.jquery);
console.log("support type:", typeof $.support);
console.log("property count:", Object.keys($.support).length);
console.log("keys:", Object.keys($.support).join(", "));

jQuery version: 3.7.1
support type: object
property count: (small set of internal flags)
keys: checkClone, clearCloneStyle, ...

Object.keys($.support).forEach(function (key) {
  var val = $.support[key];
  console.log(key + ": " + typeof val);
});

checkClone: boolean
clearCloneStyle: function
...(each key with typeof)

try {
  var json = JSON.stringify($.support);
  console.log("serialized length:", json.length);
} catch (err) {
  console.log("JSON.stringify failed:", err.message);
}

// Safer: log only key names
console.log("safe snapshot:", Object.keys($.support));

serialized length: (may omit functions)
safe snapshot: ["checkClone", ...]

// ANTI-PATTERN — $.support.opacity was removed in jQuery 1.9
function setFade(el, opacity) {
  if ($.support && $.support.opacity) {
    $(el).css("opacity", opacity);
  } else {
    $(el).css("filter", "alpha(opacity=" + (opacity * 100) + ")");
  }
}

// Modern: CSS opacity works everywhere jQuery 3 targets
console.log("opacity flag exists?", "opacity" in $.support); // false in 3.x
setFade("#box", 0.5); // .css("opacity") is fine

opacity flag exists? false

var features = {
  fetch: typeof fetch === "function",
  flexbox: window.CSS && CSS.supports("display", "flex"),
  localStorage: (function () {
    try {
      localStorage.setItem("_t", "1");
      localStorage.removeItem("_t");
      return true;
    } catch (e) {
      return false;
    }
  })()
};

console.log(features);
// Branch on features.fetch — not on $.support.ajax

{ fetch: true, flexbox: true, localStorage: true }

🚀 When You Might Encounter jQuery.support

• Reading jQuery source — understand why .clone() or .css() branches internally.
• Maintaining legacy plugins — find and remove $.support dependencies during upgrades.
• Debugging Migrate warnings — plugins that still touch removed support flags.
• Teaching browser history — see how libraries handled IE quirks before evergreen browsers.
• Version comparison — diff Object.keys($.support) between jQuery 1.x and 3.x in DevTools.
• Not for new features — always use explicit feature tests in greenfield code.

📝 Notes

• Added in jQuery 1.3; deprecated for external use in jQuery 1.9.
• Official docs: properties may be removed when no longer needed internally.
• Not JSON-serializable since jQuery 1.11 / 1.12 (function-valued entries).
• Related removed API: jQuery.browser (user-agent sniffing, removed 1.9).
• Use Modernizr or native feature detection for your project.
• jQuery Migrate plugin can help legacy code during upgrades — not a long-term strategy.
• Still present in jQuery 3.7.x — but with a much smaller, internal-only surface.

💡 Best Practices