Question

来自AngularJS isArray来源：

return toString.call(value) === '[object Array]';

为什么不跟他们一起去？

return value instanceof Array;

Answer 1

因为如果你收到来自不同window的数组（例如，另一个框架或iframe，子窗口，父窗口等），它将不会是instanceof 您的窗口中的Array构造函数。

这就是为什么在ES5中他们将Array.isArray function添加到JavaScript中，所以我们可以停止这样做，这看起来像这样：

if (Object.prototype.toString.call(theArray) === "[object Array]") ...

此各方面的示例：Live Copy

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是从父级接收数组的参数的名称）：

Got 1, 2, 3
something instanceof Array? false
Object.prototype.toString.call(something): [object Array]
Array.isArray(something)? true

为什么AngularJS在其isArray函数中不使用instanceof？

1 个答案: