javascript regexp help passing in a var to be included as part of the match

Question

Need some help from you javascript regexp pro's

I have a function that I want to pass in some a "value" and a list of accepted characters. This function works in php, but the javascript variables don't work the same as in php, so I need some guiadance.

I would like to call this function like this:

isAlphaNumeric(myValue, "_-");

This would allow any number, or letter as well as the underscore and the hyphen, but no other characters

This is the function I have, but doesn't quite work right.

function isAlphaNumeric(value, allow)
{
    var result = /^[A-Za-z0-9+allow+]+$/.test(value);
    return result;
}

How can I accomplish what I'm after?

Thanks for the help.

score 4 · Accepted Answer · answered Feb 16 '11 at 02:27

4

Use RegExp object constructor

function isAlphaNumeric(value, allow)
{
    var re = new RegExp( '^[A-Za-z0-9'+allow+']+$');
    var result = re.test(value);
    return result;
}

or

function isAlphaNumeric(value, allow)
{
    return new RegExp( '^[A-Za-z0-9'+allow+']+$').test(value);
}

answered Feb 16 '11 at 02:27

RichardTheKiwi

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You'll want to escape `allow` as well. – David Tang Feb 16 '11 at 02:39
@Box9 "allow" is not coming from end users, so we'll let that pass – RichardTheKiwi Feb 16 '11 at 02:46
@cyber, in the question the example given for `allow` was `"_-"`, which *does* need escaping ;) – David Tang Feb 16 '11 at 03:01
@Box - really? even though it is encapsulated in `^[..]` ? – RichardTheKiwi Feb 16 '11 at 03:05
@cyberwiki: JS seems to allow it, but in most PCRE, if you wish to include the dash `-` in a character class, it has to come first. (Due to it's role as a range operator.) – Orbling Feb 16 '11 at 03:20
@cyber, sorry, not for that particular example, as a `-` on the end seems to work, but you'll run into problems if another character was added, which will make `-` a special character. – David Tang Feb 16 '11 at 03:25
@Orbling - or last, as in this case. @Box9 - caller can do the escaping. – RichardTheKiwi Feb 16 '11 at 06:09

score 1 · Answer 2 · answered Feb 16 '11 at 02:27

1

By creating a RegExp() object.

function isAlphaNumeric(value, allow) {
    var re = new RegExp('^[a-z0-9' + (allow ? allow : '') + ']+$');

    return re.test(value);
}

answered Feb 16 '11 at 02:27

Orbling

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(allow ? allow : '') appears to be redundant – RichardTheKiwi Feb 16 '11 at 02:29
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@cyberkiwi: Not so, it stops things like undefined and nulls mucking up the string concatenation. – Orbling Feb 16 '11 at 02:32
@cyberwiki: Just because the results come back the same, does not mean it is doing it right, worth looking at what it does to the regexp, check this out: http://jsfiddle.net/ASVvW/2/ – Orbling Feb 16 '11 at 02:58
lol .. it does work for the question though, since both "null" and "undefined" are contained in `A-Za-z`. Luck – RichardTheKiwi Feb 16 '11 at 03:04
1

@cyberwiki: Exactly, luck saved the day for you. However, it is *always* good practice to validate incoming values to functions. – Orbling Feb 16 '11 at 03:18

score 1 · Answer 3 · edited May 23 '17 at 10:24

1

Javascript doesn't handle variables inside strings/regexs directly. You have to create the Regex using the constructor like this:

function isAlphaNumeric(value, allow)
{
    var result = new RegExp("^[A-Za-z0-9" + allow + "]+$").test(value);
    return result;
}

Tested on: http://jsfiddle.net/ZLdtw/

Check this other SO question for more info on this concatenation.

edited May 23 '17 at 10:24

Community

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answered Feb 16 '11 at 02:27

Mariano Desanze

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javascript regexp help passing in a var to be included as part of the match

3 Answers3