为什么在字符串上+++会产生奇怪的结果 [英] Why + + on strings gives strange result
问题描述
我正在使用jQuery动态附加元素，发现使用+ +时会显示NaN并且未添加下一个文本.
I was working on appending the element dynamically using jQuery and found that when using + + it shows NaN and the next text is not added.
我可以猜测+ +在这里以算术加运算符的方式工作并返回NaN.
I can guess that somehow + + works here as Arithmetic plus operator and returns NaN.
这不是增量运算符，因为两个+之间有空格.
This is not Increment operator as there is space between the two +.
我的问题是
- 这里实际上发生了什么，所以它返回
NaN - 为什么
+在被字符串包围时不能用作串联运算符.
- What is actually happening here so it returns
NaN - Why
+here does not work as concatenation operator when it is surrounded by strings.
$('#message').html('<span>' + + ' new message</span>');
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="message"></div>
在Node.js中可以看到相同的行为
The same behaviour can be seen in Node.js
> 'a' + + 'b' // aNaN
注意::我知道我在这里添加了一个额外的+并将其删除将对我有用.
Note: I know that I've added an extra + here and removing that will work for me.
推荐答案
原因是因为将+字符放在字符串之前，是您试图将'b'字符串转换为数字，结果导致NaN.您问题中的代码与此等效:
The reason is because by placing the + character before a string you're attempting to convert the 'b' string to a number, which results in NaN. The code in your question is equivalent to this:
'a' + Number('b')
因此，Number('b')返回NaN，然后将其强制为字符串并附加到a.这种行为是JS固有的，因此所使用的库(无论是jQuery，节点还是其他任何库)都是无关紧要的.
Hence Number('b') returns NaN which is then coerced to a string and appended to a. This behaviour is intrinsic to JS, so the library being used (whether jQuery, node or any other) is irrelevant.
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