To determine if an object is an array, you can either use Array.isArray()
or the instanceof
operator. While both methods work for arrays created either using the array literal syntax or the Array
constructor, there’s a key difference. Array.isArray()
is more reliable, as it works with cross-realm-objects, such as those created in an iframe
.
代码实现
let iframeEl = document.createElement('iframe');
document.body.appendChild(iframeEl);
iframeArray = window.frames[window.frames.length - 1].Array;
let array1 = new Array(1,1,1,1);
let array2 = new iframeArray(1,1,1,1);
console.log(array1 instanceof Array); // true
console.log(Array.isArray(array1)); // true
console.log(array2 instanceof Array); // false
console.log(Array.isArray(array2)); // true
As illustrated in the previous example, instanceof
breaks when working with an iframe
. However, Array.isArray()
produces the correct result regardless of the way the array was instantiated.
If you are interested in knowing why instanceof Array
doesn’t work across different globals (i.e. iframe
or window
), you can read more about it here.