JavaScript 字符串赋值运算符

发布于 2024-08-11 17:13:57 字数 245 浏览 4 评论 0原文

为什么我可以在字符串上使用 +=，但不能在字符串上使用 -=？

例如...

var test = "Test";
var arr = "&#8660;"

test += arr;
alert(test);  // Shows "Test&#8660;"

test -= arr;
alert(test);  // Shows "NaN"

原文

How come I can use += on a string, but I cannot use -= on it?

For example...

var test = "Test";
var arr = "⇔"

test += arr;
alert(test);  // Shows "Test⇔"

test -= arr;
alert(test);  // Shows "NaN"

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闻呓 2024-08-18 17:13:57

简短的答案是 - 它没有被定义为与字符串一起使用。

更长的答案：如果您尝试对两个字符串进行减法运算符，它会首先将它们转换为数字，然后执行算术运算。

"10" - "2" = 8

如果您尝试非数字的内容，您会收到 NaN 相关错误：

"AA" - "A" = NaN

The short answer is - it isn't defined to work with strings.

Longer answer: if you try the subtraction operator on two strings, it will first cast them to numbers and then perform the arithmetic.

"10" - "2" = 8

If you try something that is non-numeric, you get a NaN related error:

"AA" - "A" = NaN

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暖心男生 2024-08-18 17:13:57

因为+运算符连接字符串，而-运算符仅将数字相减。

至于为什么——可能是因为很难确定人们在字符串相减时想要做什么。

例如：

"My string is a very string-y string" - "string"

这应该做什么？

Because the + operator concatenates strings, but the - operator only subtracts numbers from each other.

As to the why -- probably because it is difficult to determine what people want to do when they subtract strings from each other.

For example:

"My string is a very string-y string" - "string"

What should this do?

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葬心 2024-08-18 17:13:57

如上所述，-= 运算符未重载以用于字符串，它仅适用于数字。

如果您尝试将其与字符串一起使用，则该运算符将尝试将两个操作数转换为 Number，这就是您得到 NaN 的原因，因为：

isNaN(+"foo"); // true

要摆脱 < test 字符串上的 code>arr 内容，您可以替换它：

var test = "Test",
    arr = "⇔"

test += arr;
alert(test);  // Shows "Test⇔"

test = test.replace(arr, ""); // replace the content of 'arr' with "" on 'test'
alert(test);  // Shows "Test"

As all said, the -= operator is not overloaded to work with Strings, it only works with Numbers.

If you try to use it with strings, the operator will try to convert both operands to Number, that is why you are getting NaN, because:

isNaN(+"foo"); // true

To get rid of the arr content on your test string, you can replace it:

var test = "Test",
    arr = "⇔"

test += arr;
alert(test);  // Shows "Test⇔"

test = test.replace(arr, ""); // replace the content of 'arr' with "" on 'test'
alert(test);  // Shows "Test"

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