Javascript .match() 与正则表达式返回 null
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.match() with a regular expression returns null
提问by MichaelH
I am trying to do something I thought would be pretty easy to do, which is to restrict a string to certain characters by matching a regular expression.
我正在尝试做一些我认为很容易做到的事情，即通过匹配正则表达式将字符串限制为某些字符。
var value = 'FailureStr1ng';
var type = 'ALPHA';
var regex = null;
switch(type) {
case 'ALPHA':
regex = '^[a-zA-Z]+$';
break;
case 'NUMERIC':
regex = '^[0-9]+$';
break;
case 'ALPHANUMERIC':
regex = '^[a-zA-Z0-9]+$';
break;
}
return value.match(regex);
For some reason, when using the match it always returns null. Is there a way to fix this, or a better method to do this?
出于某种原因，使用匹配时它总是返回null. 有没有办法解决这个问题，或者有更好的方法来做到这一点？
Note:The code here is a snippet of much larger code, and in turn the value and type variable are usually defined by another method.
注意：这里的代码是一段更大的代码，而值和类型变量通常是由另一种方法定义的。
回答by Ry-
You want RegExp.test, which tests a value for a match instead of retrieving the match. With your existing code, that would mean:
你想要RegExp.test，它测试一个匹配的值而不是检索匹配。使用您现有的代码，这意味着：
if(!new RegExp(regex).test(value)){
alert('Your string was invalid.');
}
However, it would be preferable to use RegExp literals instead of strings, as they're much more efficient and clear, and less prone to error:
但是，最好使用 RegExp 文字而不是字符串，因为它们更高效、更清晰，而且更不容易出错：
var value = 'FailureStr1ng';
var type = 'ALPHA';
var regex = null;
switch(type) {
case 'ALPHA':
regex = /^[a-zA-Z]+$/;
break;
case 'NUMERIC':
regex = /^[0-9]+$/;
break;
case 'ALPHANUMERIC':
regex = /^[a-zA-Z0-9]+$/;
break;
}
if(!regex.test(value)) {
alert('Your string was invalid.');
}
Even better, use a dictionary:
更好的是，使用字典：
var expressions = {
ALPHA: /^[a-zA-Z]+$/,
NUMERIC: /^[0-9]+$/,
ALPHANUMERIC: /^[a-zA-Z0-9]+$/
};
if(!expressions[type].test(value)) {
alert('Your string was invalid.');
}
回答by kevinji
Regex must be surrounded with /, not ', so that JavaScript creates a variable of type regex, not of type string. So for instance, for your ALPHA case, you should have
正则表达式必须用/, not包围'，以便 JavaScript 创建一个正则表达式类型的变量，而不是字符串类型的变量。因此，例如，对于您的 ALPHA 案例，您应该有
regex = /^[a-zA-Z]+$/;
See MDN's page on .matchfor more information about using .match.
请参见上MDN的页面.match有关使用的详细信息.match。
回答by Niet the Dark Absol
Your code looks like it's inside a function { ... }. Are you returning anything? If not, that's why you're getting nullback...
您的代码看起来像是在function { ... }. 你return有事吗？如果没有，这就是你null回来的原因......
Also, regexes are surrounded by slashes (/.../), not quotes.
此外，正则表达式被斜杠 ( /.../)包围，而不是引号。
