在“for(x in object)”循环中指定“x”的初始值

发布于 2024-10-10 18:03:49 字数 957 浏览 4 评论 0原文

如果我有以下代码：

<html>
    <body>
        <script type="text/javascript">
            var mycars = new Array();
            mycars[0] = "Saab";
            mycars[1] = "Volvo";
            mycars[2] = "BMW";

            var x = 1;

            document.write("Value of x: " + x + "<br /><br />");

            for (x in mycars)
            {
                document.write(x + ": " + mycars[x] + "<br />");
            }

            document.write("<br />Value of x: " + x + "<br />");
            document.write("Number of cars: " + mycars.length);
        </script>
    </body>
</html>

我得到输出：

Value of x: 1

0: Saab
1: Volvo
2: BMW

Value of x: 2
Number of cars: 3

在不将 for-in 循环更改为 for 循环的情况下，是否有任何方法可以使其不显示第一个元素（“Saab”）？我希望输出是：

Value of x: 1

1: Volvo
2: BMW

Value of x: 2
Number of cars: 3

原文

If I have the following code:

<html>
    <body>
        <script type="text/javascript">
            var mycars = new Array();
            mycars[0] = "Saab";
            mycars[1] = "Volvo";
            mycars[2] = "BMW";

            var x = 1;

            document.write("Value of x: " + x + "<br /><br />");

            for (x in mycars)
            {
                document.write(x + ": " + mycars[x] + "<br />");
            }

            document.write("<br />Value of x: " + x + "<br />");
            document.write("Number of cars: " + mycars.length);
        </script>
    </body>
</html>

I get the output:

Value of x: 1

0: Saab
1: Volvo
2: BMW

Value of x: 2
Number of cars: 3

Without changing the for-in loop to a for loop, is there any way to make it so the first element ("Saab") is not displayed? I would like the output to be:

Value of x: 1

1: Volvo
2: BMW

Value of x: 2
Number of cars: 3

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起风了 2024-10-17 18:03:49

不要使用 for..in 循环来循环数组。仅使用 for..in 来循环对象。否则可能会产生意想不到的后果，这似乎令人困惑。

使用标准的 for 循环：

for (var i = 0; i < mycars.length; i++)
{
    document.write(i + ": " + mycars[i] + "<br />");
}

如果您想错过第一个项目，请将 i 最初设置为 1，而不是 0< /代码>。您可能应该添加注释，这样当您回到这段代码时您就知道发生了什么。

Don't use for..in loops to loop through arrays. Use for..in only for looping through objects. Doing otherwise can have unintended consequences, that can seem baffling.

Use a standard for loop:

for (var i = 0; i < mycars.length; i++)
{
    document.write(i + ": " + mycars[i] + "<br />");
}

If you want to miss the first item out, set i to 1 initially, rather than 0. You should probably put a comment in, so you know what's happening if you ever come back to this bit of code.

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终难愈 2024-10-17 18:03:49

无论如何，您不应该使用 for..in 循环来遍历数组。来自 MDC：

“此外，因为迭代顺序是
任意的，迭代数组可能
不按数字顺序访问元素。”

因此，您不仅不能跳过“第一个”元素，甚至不能依赖第一个元素的一致性！

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一城柳絮吹成雪 2024-10-17 18:03:49

为了达到你想要的效果，有这样的代码：

var x = 1;
document.write("Value of x: " + x + "<br /><br />");
while (x < mycars.length) {
{
    document.write(x + ": " + mycars[x] + "<br />");
    x++;
}
x--;

document.write("<br />Value of x: " + x + "<br />");
document.write("Number of cars: " + mycars.length);

To achieve exactly what you want, have such code:

var x = 1;
document.write("Value of x: " + x + "<br /><br />");
while (x < mycars.length) {
{
    document.write(x + ": " + mycars[x] + "<br />");
    x++;
}
x--;

document.write("<br />Value of x: " + x + "<br />");
document.write("Number of cars: " + mycars.length);

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