Javascript .toLowerCase 不工作，替换功能？
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.toLowerCase not working, replacement function?
提问by Lucas
The .toLowerCasemethod is giving me an error when I try to use it on numbers. This is what I have:
.toLowerCase当我尝试在数字上使用该方法时，它给了我一个错误。这就是我所拥有的：
var ans = 334;
var temp = ans.toLowerCase();
alert(temp);
And then it gives me this error:
然后它给了我这个错误：
'undefined' is not a function (evaluating 'ans.toLowerCase()')
I don't know where I got this wrong. I always thought that numbers can also be parsed, with no change in result (maybe that's where I stuffed up).
我不知道我哪里出错了。我一直认为数字也可以解析，结果没有变化（也许这就是我塞满的地方）。
But if that's not the error, can someone write a custom makeLowerCasefunction, to make the string lower case, perhaps using regex or something?
但如果这不是错误，有人可以编写一个自定义makeLowerCase函数，使字符串小写，也许使用正则表达式或其他东西？
回答by spender
.toLowerCase function only exists on strings. You can call toString() on anything in javascript to get a string representation. Putting this all together:
.toLowerCase 函数只存在于字符串上。您可以对 javascript 中的任何内容调用 toString() 以获取字符串表示形式。把这一切放在一起：
var ans = 334;
var temp = ans.toString().toLowerCase();
alert(temp);
回答by 0x499602D2
Numbers inherit from the Numberconstructor which doesn't have the .toLowerCasemethod. You can look it up as a matter of fact:
数字从Number没有该.toLowerCase方法的构造函数继承。事实上，你可以查一下：
"toLowerCase" in Number.prototype; // false
回答by Guffa
It's not an error. Javascript will gladly convert a number to a string when a string is expected (for example parseInt(42)), but in this case there is nothing that expect the number to be a string.
这不是错误。当需要字符串时，Javascript 很乐意将数字转换为字符串（例如parseInt(42)），但在这种情况下，没有任何东西期望数字是字符串。
Here's a makeLowerCasefunction. :)
这是一个makeLowerCase函数。:)
function makeLowerCase(value) {
return value.toString().toLowerCase();
}
回答by Joe Coder
var ans = 334 + '';
var temp = ans.toLowerCase();
alert(temp);
回答by Quentin
It is a number, not a string. Numbers don't have a toLowerCase()function because numbers do not have case in the first place.
它是一个数字，而不是一个字符串。数字没有toLowerCase()功能，因为数字首先没有大小写。
To make the function run without error, run it on a string.
要使函数无错误地运行，请在字符串上运行它。
var ans = "334";
Of course, the output will be the same as the input since, as mentioned, numbers don't have case in the first place.
当然，输出将与输入相同，因为如前所述，数字首先没有大小写。
