javascript 为什么不能对 HTML 输入对象的值使用 toFixed？
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Why can't I use toFixed on an HTML input object's value?
提问by Jeff Chausse
I have an HTML input element and I'm trying to force a single decimal place into the input after the user changes the value. So, let's say the user enters "4", I run this code:
我有一个 HTML 输入元素，我试图在用户更改值后强制输入一个小数位。因此，假设用户输入“4”，我运行以下代码：
this.value = this.value.toFixed(1)
but then I get a JavaScript error saying "Object 4 has no method 'toFixed'".
但随后我收到一个 JavaScript 错误，提示“对象 4 没有‘toFixed’方法”。
It seems like JavaScript is trying to process a literal as a Number and failing but, er, why? And how do I avoid it?
似乎 JavaScript 正试图将文字作为数字处理，但失败了，呃，为什么？我该如何避免？
回答by zzzzBov
this.valueis a Stringwhen you get it from an input element. You need to cast it to a number before you can use a number's methods on it:
this.value是String，当你从一个输入元素得到它。您需要先将其转换为数字，然后才能对其使用数字的方法：
this.value = Number(this.value).toFixed(1);
Alternatively you can use the unary +operator to cast the string to a number:
或者，您可以使用一元运算+符将字符串转换为数字：
this.value (+this.value).toFixed(1);
If you need to remove string suffixes, then you could use parseFloat:
如果您需要删除字符串后缀，则可以使用parseFloat：
this.value = parseFloat(this.value).toFixed(1);
However, it's worth noting that parseFloatdoes nothandle hexadecimal formats while casting to Numberdoes:
然而，值得注意的是，parseFloat不处理的十六进制格式，而铸造Number呢：
this.value = +'0xF'; //15
this.value = parseFloat('0xF'); //0
回答by Anurag
convert to a Number first,
首先转换为数字，
this.value = Number(this.value).toFixed(1);
this.valueis a String, and a string does not have the toFixedmethod.
this.value是一个字符串，而字符串没有该toFixed方法。
