javascript 中的语句是为....
任何人都可以解释如何在 javascript 中使用 for...in 语句。我读过w3school的文章，但我认为它不太清楚。下面是代码，请解释一下：
<html>
<body>
<script type="text/javascript">
var x;
var mycars = new Array();
mycars[10] = "Saab";
mycars[20] = "Volvo";
mycars[30] = "BMW";
for (x in mycars)
{
document.write(mycars[x] + "<br />");
}
</script>
</body>
</html>
anyone can explain how to use for...in statement in javascript. I had read the w3school article but i think it is not so clear.Below is the code, please explain this:
<html>
<body>
<script type="text/javascript">
var x;
var mycars = new Array();
mycars[10] = "Saab";
mycars[20] = "Volvo";
mycars[30] = "BMW";
for (x in mycars)
{
document.write(mycars[x] + "<br />");
}
</script>
</body>
</html>
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评论（4）
for in循环将迭代对象中的每个属性。在您的示例中，
x变量将循环访问mycars对象中的每个属性。如果您添加
mycars.expense = "Porsche";，它也会发现这一点。请注意，正如MDC所述，
for in循环不应该用于循环普通数组：A
for inloop will iterate through every property in an object.In your example, the
xvariable will cycle through every property in themycarsobject.If you add
mycars.expensive = "Porsche";, it will find that too.Note that, as stated by MDC,
for inloops should not be used to loop through ordinary arrays:首先，您创建一个包含 3 个项目（而不是数组）的对象
，其中
10、20和30是对象属性。那么您想要浏览该对象，访问所有属性并显示与属性关联的每个值。
这是 [
for(variableinobject) expression ] javascript 构造的地方干预：变量将被设置为对象的第一个属性，然后是第二个属性，然后是最后一个属性。尝试
看看它是如何工作的，还有这个
First you create an object with 3 items (and not an Array)
where
10,20and30are the object properties.then you want to navigate through the object, visit all properties and display each value associated to a property.
This is where the [
for(variableinobject) expression ] javascript construction intervenes:The variable will be set to the first property of the object, then to the 2nd, then to the last. Try
to see how it works, and this as well
for ... in结构迭代in右侧对象内的每个元素。在您的例子中，for语句下面的块会针对mycars中的每辆车执行一次。The
for ... inconstruction iterates over every element within the object on the right side ofin. In your case, the block below theforstatement is executed once for every car inmycars.for in是一种埋藏bug以供后人发现的方式。正如已经大量指出的那样，如果应用于数组，它将循环遍历数组的所有元素、数组的长度以及附加到数组的任何其他数据。将其应用于普通对象会更好，但您仍然应该通过hasOwnProperty过滤索引。最好使用框架提供的函数，例如 jQuery 的
$.eachfor inis a way of burying bugs for later generations to discover. As has been copiously pointed out, if applied to an Array, it will loop through all the elements of the array, and the length of the array, and whatever other data happens to be attached to the array. Applying it to an ordinary object is better, but you still should still filter the indices throughhasOwnProperty.Better to use a framework-provided function like jQuery's
$.each