Object.keys() 在 Internet Explorer 9 中适用于内置对象吗？

发布于 2024-11-15 10:13:46 字数 835 浏览 3 评论 0 原文

Object.keys() 方法对我来说效果很好，代码如下：

var foo = {foo: 1, bar: 2};
console.log(Object.keys(foo).length);

但是，Object.keys() 为内置对象返回一个零长度数组，代码如下：

<!doctype html> 
<html>

<head>

<title>Object.keys()</title>

</head>

<body>
<script type="text/javascript">
console.log(Object.keys(window.document).length);
</script>

</body>

</html>

我错过了什么吗？我使用的是 Internet Explorer 9.0.8112.16421。

后记：我仍然不清楚为什么（例如）：

    for (prop in performance.timing) {
        if (performance.timing.hasOwnProperty(prop)) {
            console.log(prop); 
        }
    }

...在 IE9 中没有产生任何结果，而这工作正常：

for (prop in performance.timing) {
    console.log(prop); 
}

原文

The Object.keys() method works fine for me with code like this:

var foo = {foo: 1, bar: 2};
console.log(Object.keys(foo).length);

However, Object.keys() returns a zero-length array for built-in objects with code like this:

<!doctype html> 
<html>

<head>

<title>Object.keys()</title>

</head>

<body>
<script type="text/javascript">
console.log(Object.keys(window.document).length);
</script>

</body>

</html>

Am I missing something? I'm using Internet Explorer 9.0.8112.16421.

Postscript: I'm still not clear why this (for example):

    for (prop in performance.timing) {
        if (performance.timing.hasOwnProperty(prop)) {
            console.log(prop); 
        }
    }

...produces nothing in IE9, whereas this works fine:

for (prop in performance.timing) {
    console.log(prop); 
}

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东北女汉子 2024-11-22 10:13:46

在 JavaScript 中，有本机对象和宿主对象。一般来说，您可以依赖诸如 Object.keys 之类的东西来处理本机对象，但不能用于主机对象。 window、document 等都是宿主对象。 IE 尤其以其宿主对象与本机不同而闻名（宿主函数没有 call 或 apply 功能等）。

当然，也可能是 document 没有可枚举属性。对象的大多数默认属性都是不可枚举的，因此不会显示在 Object.keys 中。例如，Object.keys([]).length 和 Object.keys(new RegExp(".*")).length 都是 0因为它们都没有任何可枚举属性，即使它们都有很多属性（它们具有所有“方法”的属性，当然空白数组有一个长度 属性和 RegExp 有lastIndex 属性）。

更新：事实上，这是可枚举的事情。尝试这个测试：

alert(Object.keys(window.document).length);
window.document.AAA__expando__property = "foo";
alert(Object.keys(window.document).length);

对我来说，在 IE9 上，这些警报分别是“0”和“1”。所以 window.document 支持 Object.keys，只是 window.document 默认情况下没有任何可枚举< /em> 属性。（相比之下，在 Chrome 上，我首先获得 65 个可枚举属性，当然，一旦添加了扩展，我就获得了 66 个属性。）

这是一个更完整的测试页面 (Live Copy)（快速拼凑在一起，不美观）：

window.onload = function() {

  document.getElementById('theButton').onclick = function() {

    if (typeof Object.keys !== 'function') {
      display("<code>Object.keys</code> is not a function");
      return;
    }
    showKeys("Before adding", Object.keys(window.document));
    window.document.AAAA__expando__foo = "bar";
    showKeys("After adding", Object.keys(window.document));
  };

  function showKeys(prefix, keys) {
    var p, ul;

    keys.sort();
    prefix =
      "[" + prefix +
      "] Keys on <code>window.document</code> (" +
      keys.length +
      ")";
    if (keys.length !== 0) {
      prefix += " (click to toggle list)";
    }
    p = display(prefix);
    if (keys.length !== 0) {
      ul = document.createElement("ul");
      ul.innerHTML = "<li>" + keys.join("</li><li>") + "</li>";
      ul.style.display = "none";
      document.body.appendChild(ul);
      p.onclick = function() {
        ul.style.display =
          (ul.style.display === "none") ? "" : "none";
      };
    }
  }

  function display(msg) {
    var p = document.createElement('p');
    p.innerHTML = msg;
    document.body.appendChild(p);
    return p;
  }

};

In JavaScript, there are native objects and host objects. In general, you can rely on things like Object.keys working with native objects, but not with host objects. window, document, and others are host objects. IE in particular is well-known for its host objects not being native-like (host functions don't have the call or apply feature, etc.).

Alternately, of course, it could be that document has no enumerable properties. Most of the default properties of objects are non-enumerable and so don't show up in Object.keys. For instance, Object.keys([]).length and Object.keys(new RegExp(".*")).length are both 0 because neither has any enumerable properties even though they both have lots of properties (they have properties for all of their "methods", and of course the blank array has a length property and the RegExp has a lastIndex property).

Update: And in fact, it was the enumerable thing. Try this test:

alert(Object.keys(window.document).length);
window.document.AAA__expando__property = "foo";
alert(Object.keys(window.document).length);

For me, on IE9, those alerts are "0" and "1", respectively. So window.document supports Object.keys, it's just that window.document doesn't, by default, have any enumerable properties. (In contrast, on Chrome I get 65 enumerable properties to start with, and of course 66 once I've added my expando.)

Here's a rather more full test page (live copy) (hacked-together quickly, not a thing of beauty):

window.onload = function() {

  document.getElementById('theButton').onclick = function() {

    if (typeof Object.keys !== 'function') {
      display("<code>Object.keys</code> is not a function");
      return;
    }
    showKeys("Before adding", Object.keys(window.document));
    window.document.AAAA__expando__foo = "bar";
    showKeys("After adding", Object.keys(window.document));
  };

  function showKeys(prefix, keys) {
    var p, ul;

    keys.sort();
    prefix =
      "[" + prefix +
      "] Keys on <code>window.document</code> (" +
      keys.length +
      ")";
    if (keys.length !== 0) {
      prefix += " (click to toggle list)";
    }
    p = display(prefix);
    if (keys.length !== 0) {
      ul = document.createElement("ul");
      ul.innerHTML = "<li>" + keys.join("</li><li>") + "</li>";
      ul.style.display = "none";
      document.body.appendChild(ul);
      p.onclick = function() {
        ul.style.display =
          (ul.style.display === "none") ? "" : "none";
      };
    }
  }

  function display(msg) {
    var p = document.createElement('p');
    p.innerHTML = msg;
    document.body.appendChild(p);
    return p;
  }

};

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