因为如果你从不同的地方收到一个数组window（例如，另一个框架或 iframe、子窗口、父窗口等），它不会instanceof the Array构造函数在your window.
这就是为什么他们在 ES5 中添加了Array.isArray功能 http://www.ecma-international.org/ecma-262/5.1/#sec-15.4.3.2到 JavaScript，所以我们可以停止以困难的方式做这件事，如下所示：
if (Object.prototype.toString.call(theArray) === "[object Array]") ...
各个方面的示例：实时复制 http://jsbin.com/vejot/1
父窗口：
<body>
<input type="button" value="Click To Open Window">
<script>
(function() {
"use strict";
var wnd;
document.querySelector("input").onclick = function() {
wnd = window.open("http://jsbin.com/yimug/1");
display("Opened, waiting for child window to load...");
setTimeout(waitForChild, 10);
};
function waitForChild() {
if (wnd && wnd.sendMeSomething) {
display("Child window loaded, sending [1, 2, 3]");
wnd.sendMeSomething([1, 2, 3]);
}
}
function display(msg) {
var p = document.createElement('p');
p.innerHTML = String(msg);
document.body.appendChild(p);
}
})();
</script>
</body>
子窗口：
<script>
(function() {
"use strict";
window.sendMeSomething = function(something) {
display("Got " + something.join(", "));
display("something instanceof Array? " + (something instanceof Array));
display("Object.prototype.toString.call(something): " + Object.prototype.toString.call(something));
if (Array.isArray) {
display("Array.isArray(something)? " + Array.isArray(something));
}
};
function display(msg) {
var p = document.createElement('p');
p.innerHTML = String(msg);
document.body.appendChild(p);
}
})();
</script>
输出（在子窗口中）(something是参数的名称，它从父级接收数组）:
Got 1, 2, 3
something instanceof Array? false
Object.prototype.toString.call(something): [object Array]
Array.isArray(something)? true
