js：请用5个双引号说明该变量值 [英] js: please explain this variable value with 5 double quotations

问题描述

请简要看一下下面的代码：

Please, take a brief look at the code below:

<script type="text/javascript">
function recentpostslist(json) {
 document.write('<ul class="recommended">');
 var i;
 var j;
 for (i = 0; i < json.feed.entry.length; i++)
 {
  for (j = 0; j < json.feed.entry[i].link.length; j++) {
   if (json.feed.entry[i].link[j].rel == 'alternate') {
    break;
   }
  }
var postUrl = "'" + json.feed.entry[i].link[j].href + "'";//bs
var postTitle = json.feed.entry[i].title.$t;
var item = "<li>" + "<a href="+ postUrl + '" target="_blank">' + postTitle + "</a> </li>";
 document.write(item);
 }
 document.write('</ul>');
 }
</script>
<script src="https://xxxxxxxxxx.blogspot.com/feeds/posts/summary/-/recommended?max-results=3&alt=json-in-script&callback=recentpostslist"></script>

背景信息

我在Internet上的某个地方找到了 昨天，并且一直在尝试对其进行一些修改。

Background info

I found this somewhere on the Internet yesterday, and have been trying to modify it a bit, since.

变量 i 和 j 最初是在 for 循环中声明的，例如...

Variables i and j were originally declared within the for loop, as in...

for (var i = 0; i < json.feed.entry.length; i++)
{
 for (var j = 0; j < json.feed.entry[i].link.length; j++) {
  if (json.feed.entry[i].link[j].rel == 'alternate') {
   break;
  }
 }

...

...但是一个在（初学者）读了 w3schools.com 后，我得到了他们建议将变量声明保留在 for 循环之外。我的编程技能最好的时候还很少，所以说实话，我不知道我的印象是否正确。

...but after doing a bit of (beginners') reading on w3schools.com, I got the impression that they're recommending keeping the variables declaration outside the for loop. My programming skills are scant, at their very best, so truth be told, I have no idea whether my impression was right.

然后我为<$开头的c $ c>< ul> 元素（第三行）。

Then I assigned a class to the <ul> element at the beginning (3rd line).

到目前为止，很好。我检查了一下，脚本仍然有效。

So far, so good. I checked, and the script was still working.

它的作用是列出博客的3篇最新文章的标题，这些文章被标记为推荐。

What it does is list the titles of a blog's 3 latest posts that have been labeled "recommended".

然后我尝试将一个类分配给声明为...的< li> 元素。 。第15行的 item 变量的部分值（我理解吗？）：

Then I made an attempt to assign a class to the <li> element that's declared as a... ehm... part of the value (have I understood that right?) of the item variable on line 15:

var item = "<li>" + "<a href="+ postUrl + '" target="_blank">' + postTitle + "</a> </li>";

但这似乎使代码无效，这不足为奇，

But that seems to invalidate the code, which came as no surprise, really, since it did seem like a bit of a long shot.

近距离拍摄时确实如此看看这行代码，但是，我必须说我对所有引号（单引号和双引号）都感到困惑。

When taking a closer look at this line of code, however, I must say I was quite baffled by all the quotation marks (single and double).

如果有人可以说明

< a href = + postUrl +' target = _ blank>'

为什么总共有5条双引号？

' target = _ blank>'具有什么功能？

It would be greatly appreciated if someone could explain
"<a href="+ postUrl + '" target="_blank">'
Why are there 5 double quotations in total? Is it incorrect?
What function does '" target="_blank">' serve?

推荐答案

它只是使用单引号来避免必须在双引号字符串中转义字面双引号。

It's just using single quotes to avoid having to escape the literal double quotes in a double-quoted string.

'" target="_blank"'

vs

"\"target=\"_blank\""

由于 postUrl 的定义包括该属性的引号，因此您的 item 中有一个额外的双引号，但是，我建议不将这些引号放在 postUrl 内，因为引号不是URL的部分。

Since the definition of postUrl includes the quotes for the attribute, your definition of item has an extra double quote in it. However, I would recommend not putting those quotes postUrl, because the quotes are not part of the URL.

如果这样做，该行前面会缺少双引号。您有

If you do that, there is a missing double quote earlier in the line. You have

var item = "<li>" + "<a href=" + postUrl + '" target="_blank">' + postTitle + "</a> </li>";

，您应该拥有

var item = "<li>" + '<a href="' + postUrl + '" target="_blank">' + postTitle + "</a> </li>";
                  # ^^^^^^^^^^^
                  # Include a literal " after the =,

$ b $之后包含一个文字 b

（否则，目标之前的引号是多余的，需要删除。）

(Otherwise, the quote preceding target would be extraneous and need to be removed.)

该行会更清晰一些

var item = '<li> <a href="'+ postUrl + '" target="_blank">' + postTitle + "</a> </li>";

您可以责怪JavaScript没有内置的，方便的将值插值到字符串的方法。（尽管，请参阅如何在JavaScript中进行字符串插值？，这表明已添加。请注意，我不是Javascript程序员。

and you can blame JavaScript for not having a built-in, convenient way to interpolate values into a string. (Although, see How can I do string interpolation in JavaScript?, which suggests that this has been added. Note, I am not a Javascript programmer.

var item = `<li> <a href="${postUrl}" target="_blank">${postTitle}</a> </li>`;

）

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