Check if specific chars were written and trigger an error

Question

Im trying to figure out via JS if invalid chars were entered in a textarea

I want to allow only this chars:

A-Za-z0-9 !#%&*()+-=,.?"';:/

If illegal chars were entered, I want to retrieve the bad chars, and trigger an error, i.e:

Invalid text, bad chars were written:

1) _
2) @
etc...

Thanks!

if you are ok with using jquery - http://stackoverflow.com/questions/2812585/jquery-validate-characters-on-keypress — potatopeelings, Jul 12 '10 at 10:04
It wasn't clear, do you want to allow a space? What about an underscore? — Brock Adams, Jul 12 '10 at 10:36
no underscore, allow spaces . this are the only chars i want to allow: A-Za-z0-9 !#%&*()+-=,.?"';:/ — WEBProject, Jul 12 '10 at 10:39

Tim Down · Accepted Answer · 2010-07-12T11:24:09.347

2

I'm not sure when you want to do this check, but here's a function to do the checking. It will alert the first non-valid character.

function checkValue(input) {
    var result = /[^a-z0-9 !#%&*()+\-=,.?"';:\/]/i.exec(input.value);
    if (result) {
        alert("Character '" + result[0] + "' is not allowed");
        return false;
    } else {
        return true;
    }
}

If you want all the matched non-valid characters, then you could use the following:

function checkValue(input) {
    var isValid = true, result, matchedChars = [];
    while( (result = /[^a-z0-9 !#%&*()+\-=,.?"';:\/]/ig.exec(input.value)) ) {
        matchedChars.push("'" + result[0] + "'");
        isValid = false;
    }
    if (!isValid) {
        alert("Characters " + matchedChars.join(", ") + " are not allowed");
    }
    return isValid;
}

edited Jul 12 '10 at 11:24

answered Jul 12 '10 at 10:36

Tim Down

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This regex doesn't allow spaces, which the OP said he wanted. – Brock Adams Jul 12 '10 at 11:00
So he did, I missed that. Though I think the OP did edit the question to make that clearer after I'd started writing my answer. Anyway, fixed now. – Tim Down Jul 12 '10 at 11:09
you don't need to escape dots or quantifiers inside the character class – SilentGhost Jul 12 '10 at 11:10
However, you *do* need to escape hyphens if they're in the middle (like they are here - the range `+-=` means `<` will be incorrectly included). – Peter Boughton Jul 12 '10 at 11:18
SilentGhost, Peter: good points, thanks. Also, there's no need to escape parentheses inside a character class. Fixed now. – Tim Down Jul 12 '10 at 11:24

Check if specific chars were written and trigger an error

1 Answers1