Question

I am working on an application using MVC 3 and knockoutjs library. Also I am reseraching the knockout validation plugin. I need to validate an input text value for allowed symbols. As far as I can see, there are not native rules for these so I will have to create a custom one. The bad thing is that my knowledge in regular expressions and javascript is very poor. I need to write a custom function that validates a text box input field and does not allow non-english characters. All the other symbols are permitted. I think I will be able to create the custom rule, but I need the regular expression that validates the input field. Any help with a working example will be greatly appreciated. Thank You!

Answer 1

does not allow non-english characters

and

All the other symbols are permitted

seems contradicting to me but I’ll try to help 🙂

First you should consider using Ajax for validation since server-side languages usually have much better support for Unicode. If it’s not an option then first add XRegExp library with Unicode plugin to your page.

To create a Unicode-aware regular expression use the following form:

var englishLettersOrSymbols = XRegExp('[\\p{^Letter}\\p{Latin}]*');

Here we say that we accept zero or several (... *) symbols and each symbol is either ([ ... ]) non-letter (\\p{^Letter}) or letter from basic Latin alphabet (\\p{Latin}).

Now your custom validation rule would look like this:

ko.validation.rules['englishLettersOrSymbols'] = {
    validator: function(value){
        var rule= XRegExp('[\\p{^Letter}\\p{Latin}]*');
        return rule.test(value);
    },
    message: 'Sorry, {0} this is not valid'
};

and you would use it in your code like this:

var vewModel = {
    // ...
    myField: ko.observable().extend({englishLettersOrSymbols: true}),
    // ...
};

---

Edit: Removed | from regexp. Thanks, @slevithan. It wasn’t an error per se since \\p{^Letter} already included | symbol and, thus, the regular expression would still work. However, it was quite misleading.