javascript 测试字段值是否为数字且不为空

Test if field value is numeric and not empty

提问by Vangel Tzo

Possible Duplicate:
Validate that a string is a positive integer

可能的重复：
验证字符串是否为正整数

So I want to check a form field if it's empty and to allow it to has only positive numeric numbers, no spaces or letters. So far I succeed the first part to check if the field is empty with the following code:

所以我想检查一个表单域是否为空，并允许它只有正数字，没有空格或字母。到目前为止，我使用以下代码成功检查了该字段是否为空的第一部分：

function validate(form) {
    var elements = form.elements;

    if (form.qty.value == "") {
        alert("Please enter the field");
        document.forms[0].qty.focus()
        document.forms[0].qty.select()
        return false;
    }

    return true;
}

Somewhere in the form:

某处的形式：

<form action="addtocart.php" method ="post" onsubmit="return validate(this);" />...

<form action="addtocart.php" method ="post" onsubmit="return validate(this);" />...

But now I want to allow only numbers as well as to check if the field is empty. I have found some scripts but I don't know how to merge the code into one valid script.

但现在我只想允许数字以及检查该字段是否为空。我找到了一些脚本，但我不知道如何将代码合并为一个有效的脚本。

回答by Levi Botelho

if (Number(form.qty.value) > 0) {
    // Only executes if value is a positive number.
}

Note that if the value is an empty string the statement will not return true. The same goes for null, NaN(obviously) and undefined. String representations of numbers are transformed into their numeric counterparts.

请注意，如果该值为空字符串，则该语句将不会返回 true。这同样适用于null，NaN（显然）和undefined。数字的字符串表示被转换为它们的数字对应物。

回答by shift66

you can use regexp
your pattern is ^\d+$.

你可以使用正则表达式
你的模式是^\d+$。

^- starting of the line
$- end of the line
\d- digit
+- 1 or more times

^- 行首
$- 行尾
\d- 数字
+- 1 次或多次

if(mystr.match(/^\d+$/))
{
    //
}

if you need the first symbol not to be 0you should write /^(0|[^1-9]\d*)/
read regexp documentation to understand this pattern.

如果您不需要第一个符号，0您应该编写/^(0|[^1-9]\d*)/
阅读正则表达式文档来理解这种模式。

回答by CoursesWeb

Try with search()function and RegExp. Like this:

尝试使用search()函数和 RegExp。像这样：

if (form.qty.value.search(/^([0-9\.]+)$/)==-1)
{
alert ("Please enter the field");
document.forms[0].qty.focus()
document.forms[0].qty.select()
return false;
}

回答by Aadit M Shah

Check the following answer: https://stackoverflow.com/a/10270826/783743

检查以下答案：https: //stackoverflow.com/a/10270826/783743

In your case I would do the following:

在您的情况下，我会执行以下操作：

function validate(form) {
    return isPositive(+form.qty.value);
}

function isPositive(n) {
    return +n === n && n >= 0;
}

Explanation:

解释：

1. The expression +form.qty.valuecoerces the string to a number. If the string is empty or is not a number it will express NaN.
2. The function isPositiveonly returns positive if nis a number (+n === n) and it's greater than or equal to zero (n >= 0).

1. 该表达式+form.qty.value将字符串强制转换为数字。如果字符串为空或不是数字，它将表示NaN.
2. isPositive如果n是数字 ( +n === n) 并且大于或等于零( )，则该函数仅返回正数n >= 0。