检查文本框值是字符串还是javascript中的数字 [英] Check if a textbox value is a string or a number in javascript

问题描述

基本上我有以下代码：

<input type="text" value="123" id="txtbox">
<script>
var myVar = document.getElementById('txtbox').value;

if (myVar.substring) {
alert('string');
} else{
alert('number');
}
</script>

无论您在文本框中输入什么值，它都会始终提醒字符串。有没有办法，如果你在文本框中放一个数字，它会提醒数字而不是字符串？谢谢。

No matter what value you put in the textbox, it will always alert string. Is there a way that if you put a number in the textbox it will alert number instead of string? Thank you.

推荐答案

值 on 输入元素始终一个字符串。它可能是一串数字。

value on input elements is always a string. It might be a string of digits.

如果你想知道该字符串是否只包含有效数字，你必须解析它（并决定你认为什么是有效数字） ，并且允许那样）。

If you want to know whether that string only contains valid numbers, you have to parse it (and decide what you consider a valid number, and allow for that).

例如，你会让人们告诉你使用 parseInt（myVar）或一元 + （ + myVar ）或 isNaN（myVar）（其中一元 + 的确如此）或数字（myVar）（相同），但：

For instance, you'll get people telling you to use parseInt(myVar) or the unary + (+myVar) or isNaN(myVar) (which does what the unary + does) or Number(myVar) (same), but:

1. parseInt 仅解析开头的字符串 parseInt（345foo）是 345

1. parseInt only parses the beginning of the string, parseInt("345foo") is 345

parseInt 当然只适用于整数;对于小数部分的数字你想要 parseFloat

parseInt is, of course, only for whole numbers; you'd want parseFloat for numbers with fractional portions

所有这些都无法理解成千上万的分隔符

All of those will fail to understand thousands separators

所有这些都无法理解不是的小数点分隔符。（例如，许多语言环境是，，有时甚至是空格）

All of those will fail to understand a decimal separator that isn't . (e.g., in many locales it's , or sometimes even a space)

+ myVar 和 Number（myVar）和 isNaN（myVar）等会将空字符串视为 0

+myVar and Number(myVar) and isNaN(myVar) and such will treat an empty string as 0

......那种事情。所以你必须根据你想接受的输入对字符串做一些准备。

...that kind of thing. So you have to do some prep on the string according to what input you want to accept.

一旦你决定要处理什么格式，就有一个这里有关于做实际解析的答案的十几个问题：

Once you've decide what format(s) to handle, there are a dozen questions with answers here about doing the actual parsing:

• 如何在JavaScript中将字符串转换为整数？ （注意整数-specific）


• 在JavaScript中将字符串转换为数字的最快方法是什么？

• How do I Convert a String into an Integer in JavaScript? (note that's integer-specific)
• What's the fastest way to convert String to Number in JavaScript?

这篇关于检查文本框值是字符串还是javascript中的数字的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！