jQuery jQuery.isArray() Method

What You’ll Learn

The jQuery.isArray() utility returns true when a value is a genuine JavaScript array — not merely array-like. This tutorial covers syntax, five worked examples, comparisons with Array.isArray() and $.type(), and guard patterns before calling jQuery array utilities.

Introduction

Before you filter, merge, or search with jQuery array utilities, you need to know whether the input is actually an array. The expression typeof [] returns "object", which also matches plain objects, dates, and null — so it cannot reliably answer the question.

jQuery provides jQuery.isArray() (also written $.isArray()) as a focused boolean test. It returns true only for real Array instances and false for everything else — including array-like objects that have a length property but lack array methods.

Understanding the jQuery.isArray() Method

jQuery.isArray(obj) is equivalent to jQuery.type(obj) === "array". Internally jQuery inspects the value’s internal class tag — the same mechanism that makes $.type([]) return "array" instead of "object".

Use it in plugin code, AJAX handlers, and validation logic whenever you need a clear yes/no before calling $.grep(), $.merge(), or native methods like .map() and .filter().

📝 Syntax

General form of jQuery.isArray:

jQuery.isArray( obj )
// or
$.isArray( obj )

Parameters

• obj — any JavaScript value to test.

Return value

• true if obj is a true JavaScript Array.
• false for all other values — objects, primitives, array-like collections, and null.

Minimal workflow

if ($.isArray(items)) {
  var filtered = $.grep(items, function (n) { return n > 0; });
}

Examples Gallery

Each example uses $.isArray(). Open DevTools or use the Try-it links to run them interactively.

console.log($.isArray([]));  // true
console.log($.isArray({}));  // false

true
false

var nodeList = document.querySelectorAll("p");
var $items   = $("p");
var realArr  = $.makeArray(nodeList);

console.log($.isArray(nodeList)); // false
console.log($.isArray($items));   // false
console.log($.isArray(realArr)); // true — after makeArray

false
false
true

function filterPositive(input) {
  var arr = $.isArray(input) ? input : $.makeArray(input);
  return $.grep(arr, function (n) { return n > 0; });
}

console.log(filterPositive([0, 1, 2]));           // [1, 2]
console.log(filterPositive({ 0: 0, 1: 3, length: 2 })); // [3]

[1, 2]
[3]

var data = [1, 2, 3];

console.log($.isArray(data));        // true
console.log(Array.isArray(data));    // true
console.log($.type(data) === "array"); // true
console.log(typeof data);            // "object"

true
true
true
object

function initList(options) {
  options = options || {};
  var items = options.items;

  if (!$.isArray(items)) {
    console.warn("items must be an array — got " + $.type(items));
    items = [];
  }

  return items.length;
}

console.log(initList({ items: ["a", "b"] })); // 2
console.log(initList({ items: "oops" }));     // 0 (warned)

2
0 (console warns: items must be an array)

🚀 Common Use Cases

• Plugin option validation — ensure list options are true arrays before iteration.
• AJAX response checks — confirm JSON parsed to an array before mapping results.
• Utility preconditions — guard calls to $.grep, $.merge, and $.inArray.
• Array-like conversion — branch to $.makeArray when isArray is false.
• Defensive coding — avoid calling native .map() on non-arrays.
• Legacy jQuery projects — consistent checks before ES5 Array.isArray was universal.

📝 Notes

• Available since jQuery 1.3.
• Equivalent to jQuery.type(obj) === "array".
• jQuery 3+ uses native Array.isArray when the browser supports it.
• Does not mutate the value — read-only test.
• Sparse arrays and empty arrays still return true.
• Related: $.makeArray() to convert array-like values; $.type() for full type strings.

💡 Best Practices