javascript 5 位 zip 或空的 RegEx
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RegEx for 5 digit zip or empty
提问by Registered User
I have this regex that checks for a 5 digit number ^\d{5}$
我有这个正则表达式可以检查 5 位数字 ^\d{5}$
How do I change it so that it returns true also for an empty string?
如何更改它以便它也为空字符串返回 true？
<script type="text/javascript">
var regex = /^\d{5}$/;
alert(regex.test(12345));
alert(regex.test(''));
</script>
回答by Michael Berkowski
Enclose it in ()and add a ?to make the entire pattern optional. Effectively, you are then either matching ^\d{5}$OR ^$(an empty string).
将其括起来()并添加 a?以使整个模式可选。实际上，您要么匹配^\d{5}$OR ^$（空字符串）。
var regex = /^(\d{5})?$/;
console.log(regex.test(12345));
console.log(regex.test(''));
// true
// true
// Too long, too short
console.log(regex.test(123456));
console.log(regex.test('1'));
// false
// false
Note that unless you intend to do something with the 5 digits other than prove they are present, you can use a non-capturing group (?: )to save a tiny bit of resources.
请注意，除非您打算对这 5 位数字做一些事情而不是证明它们存在，否则您可以使用非捕获组(?: )来节省一点资源。
var regex = /^(?:\d{5})?$/;
