Javascript RegEx to return if string contains characters that are NOT in the RegEx

Question

I have a user created string. I am only allowing the characters A-Z, a-z, 0-9, -, and _

Using JavaScript, how can I test to see if the string contains characters that are NOT these? If the string contains characters that are not these, I want to alert the user that it is not allowed.

What Javascript methods and RegEx patterns can I use to match this?

Donut · Accepted Answer · 2011-10-31 19:42:09Z

15

You need to use a negated character class. Use the following pattern along with the match function:

[^A-Za-z0-9\-_]

Example:

var notValid = 'This text should not be valid?';

if (notValid.match(/[^A-Za-z0-9\-_]/))
   alert('The text you entered is not valid.');

edited Oct 31, 2011 at 19:42

answered Oct 31, 2011 at 19:36

Donut

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2 Comments

James Glass Over a year ago

Thats the pattern, but what Javascript method can I use? Thank you

Matt Ball Over a year ago

@John: read the documentation. developer.mozilla.org/en/JavaScript/Guide/Regular_Expressions and regular-expressions.info/javascript.html

Ray Toal · Accepted Answer · 2011-10-31 19:38:27Z

6

This one is straightforward:

if (/[^\w\-]/.test(string)) {
    alert("Unwanted character in input");
}

The idea is if the input contains even ONE disallowed character, you alert.

answered Oct 31, 2011 at 19:38

Ray Toal

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1 Comment

Joel Peltonen Over a year ago

Just to clarify for people like me: /[^\w\-]/ - this cotains the whitelist, meaning the list of allowed characters. To add something to it, append it after the dash, for example like so: /[^\w\-äöÄÖ]/.

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