为什么我不能使用toFixed在HTML输入对象的值上？ [英] Why can't I use toFixed on an HTML input object's value?

问题描述

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。所以，假设用户输入4，我运行这段代码：

  this.value = this.value.toFixed 1）
  

但是我得到一个JavaScript错误，提示Object 4 has no method'toFixed'。

似乎JavaScript正在试图将一个文字处理为一个数字并且失败，但呃，为什么？如何避免它？

解决方案

this.value 是一个字符串当你从一个输入元素获得它时。您需要将其转换为数字，然后才能使用数字的方法：

  this.value = Number（this。值）.toFixed（1）; 
  

或者，您可以使用一元 + 运算符将字符串强制转换为数字：

  this.value（+ this.value）.toFixed（1）; 
  

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）; 
  

然而值得注意的是 parseFloat 不会处理十六进制格式，而转换为数字 不会：



  this.value = +'0xF'; // 15 
 this.value = parseFloat（'0xF'）; // 0 
  




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:

this.value = this.value.toFixed(1)

but then I get a JavaScript error saying "Object 4 has no method 'toFixed'".

It seems like JavaScript is trying to process a literal as a Number and failing but, er, why? And how do I avoid it?

解决方案

this.value is a String when 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 = Number(this.value).toFixed(1);

Alternatively you can use the unary + operator to cast the string to a number:

this.value (+this.value).toFixed(1);

If you need to remove string suffixes, then you could use parseFloat:

this.value = parseFloat(this.value).toFixed(1);

However, it's worth noting that parseFloat does not handle hexadecimal formats while casting to Number does:

this.value = +'0xF'; //15
this.value = parseFloat('0xF'); //0

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