Difficulties with constructing this JavaScript regex

Question

I would like to construct a regular expression that matches any letter (including accented and Greek), number, hyphens and spaces with a total allowed characters length between 3 and 50.

This is what I made:

[- a-zA-Z0-9çæœáééíóúžàèìòùäëïöüÿâêîôûãñõåøαβγδεζηθικλμνξοπρστυφχψωÇÆŒÁÉÍÓÚŽÀÈÌÒÙÄËÏÖÜŸÂÊÎÔÛÃÑÕÅØΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΠΡΣΤΥΦΧΨΩ]{3,50}

Now I wan't to adjust the expression so that it can't start with a hyphen or space. It will be used to validate a username.

I thought about using a negative lookbehind but these are the limitations:

JavaScript doesn't support a lookbehind.
The alternatives for a lookbehind aren't really applicable since they all depend on other JavaScript functions and I am bound to using the match function.

I hope there are any regular expression heroes here since it doesn't look simple.

Just a tip: Check which unicode ranges the greek (and other letters) are in. You could than replace the long character list by \uxxxx-\uyyyy. — Felix Kling
– Felix Kling, Commented Feb 15, 2011 at 22:50
This isn't a solution, but since nobody has said it yet, I want to make sure that you aren't solely using javascript to validate the user input. You should definitely have some backend code that replicates the frontend validation. — Keith
– Keith, Commented Feb 15, 2011 at 22:52
That was the plan. Thanks for the reminder. Actually there will be three types of validation depending on the browser: JavaScript validation or HTML5 browser validation and PHP validation. — DADU
– DADU, Commented Feb 15, 2011 at 22:54
@Felix Kling - Your tip is worth gold. Imagine typing all those characters manually. — DADU
– DADU, Commented Feb 16, 2011 at 0:34

Tim · Accepted Answer · 2011-02-15 22:46:33Z

2

I replaced your long character class with a-z for readability:

[a-z][- a-z]{2,49}

You could also match with your current regex and then make sure that the string does not match ^[ -] in another match.

answered Feb 15, 2011 at 22:46

Tim

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2 Comments

DADU Over a year ago

Seems to work but there's no option to prevent the whole a-z part from being duplicated? Since it's so long it would make it a lot more difficult to maintain.

Keith Over a year ago

you can use new RegExp(regex) if you want to convert a string to regular expression. This will allow you to set up your pattern in a string and manipulate/duplicate however you want.

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