Array.isArray()
The Array.isArray()
method determines whether the passed
value is an Array
.
Array.isArray([1, 2, 3]); // true
Array.isArray({foo: 123}); // false
Array.isArray('foobar'); // false
Array.isArray(undefined); // false
Syntax
Array.isArray(value)
Parameters
value
-
The value to be checked.
Return value
true
if the value is an Array
; otherwise,
false
.
Description
If the value is an Array
, true
is returned; otherwise,
false
is.
See the article
"Determining with absolute accuracy whether or not a JavaScript object is an array"
for more details.
Given a TypedArray
instance, false
is always returned.
Examples
Using Array.isArray
// all following calls return true
Array.isArray([]);
Array.isArray([1]);
Array.isArray(new Array());
Array.isArray(new Array('a', 'b', 'c', 'd'));
Array.isArray(new Array(3));
// Little known fact: Array.prototype itself is an array:
Array.isArray(Array.prototype);
// all following calls return false
Array.isArray();
Array.isArray({});
Array.isArray(null);
Array.isArray(undefined);
Array.isArray(17);
Array.isArray('Array');
Array.isArray(true);
Array.isArray(false);
Array.isArray(new Uint8Array(32));
Array.isArray({ __proto__: Array.prototype });
instanceof
vs isArray
When checking for Array
instance, Array.isArray
is preferred
over instanceof
because it works through iframes
.
const iframe = document.createElement('iframe');
document.body.appendChild(iframe);
xArray = window.frames[window.frames.length-1].Array;
const arr = new xArray(1,2,3); // [1,2,3]
// Correctly checking for Array
Array.isArray(arr); // true
// Considered harmful, because doesn't work through iframes
arr instanceof Array; // false
Specifications
Specification |
---|
ECMAScript Language Specification # sec-array.isarray |
Browser compatibility
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