How to concatenate string literals in javascript regular expression?

Question

I have the following expression,

var exp = new RegExp('^[a-zA-Z0-9]' + getMinMax() + '$');

My getMinMax() function returns the value dynamically ex {2,5} , etc!

But it returns an exception, it says that syntax error in regular expression. How can i correct it?

function getMinMax() {
   var minLength = Rule.MinimumLength,maxLength = Rule.MaximumLengh;
   var limitExpression = (minLength != 'undefined' && minLength != null ) ? minLength.toString() : '';

   limitExpression = (maxLength != 'undefined' && maxLength != null ) ? (limitExpression != '' && limitExpression != null) ? ('{' + limitExpression + ',' + maxLength.toString() + '}') : ('{' + maxLength.toString() + '}') : '';

   return limitExpression;
}

It works just fine, are you sure getMinMax() returns the string "{2,5}"? — João Silva
– João Silva, Commented Sep 13, 2012 at 14:00
i am dynamically getting the minlength and maxlength from the database and assign it throught getMaxMin() but it throws an exception? — ARULJOTHI PARTHIBAN
– ARULJOTHI PARTHIBAN, Commented Sep 13, 2012 at 14:01
Show us your getMinMax function… What do you mean by "database" - that sounds like an async task? — Bergi
– Bergi, Commented Sep 13, 2012 at 14:02
Set a breakpoint. Check the return value of getMinMax(). I guarantee you it is something other than {x, y}. — verdesmarald
– verdesmarald, Commented Sep 13, 2012 at 14:02
function getMinMax() { var minLength = Rule.MinimumLength,maxLength = Rule.MaximumLengh; var limitExpression = (minLength != 'undefined' && minLength != null ) ? minLength.toString() : ''; limitExpression = (maxLength != 'undefined' && maxLength != null ) ? (limitExpression != '' && limitExpression != null) ? ('{' + limitExpression + ',' + maxLength.toString() + '}') : ('{' + maxLength.toString() + '}') : ''; return limitExpression; } — ARULJOTHI PARTHIBAN
– ARULJOTHI PARTHIBAN, Commented Sep 13, 2012 at 14:02

verdesmarald · Accepted Answer · 2012-09-13 14:20:29Z

2

Your code works just fine.

My bet is that you have a small typo in your Rule object, so instead of Rule.MaximumLengh, you should probably have Rule.MaximumLength.

Also, as a suggestion, don't use so many chained ternary operators, it was really hard to read them.

edited Sep 13, 2012 at 14:20

verdesmarald

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answered Sep 13, 2012 at 14:06

João Silva

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1 Comment

verdesmarald Over a year ago

For some definition of "works", I suppose. With just a minimum it returns a blank string instead of {x,}, and just a maximum it returns {x} instead of {0,x}. I agree it shouldn't result in a regex parse error though.

mplungjan · Accepted Answer · 2012-09-13 14:29:46Z

0

can you try

function getMinMax() {
   var minLength = Rule.MinimumLength,
       maxLength = Rule.MaximumLength,
       limitExpression = "";

       if (minLength != 'undefined' && minLength != null ) {
         limitExpression += minLength.toString();
       }
       if (maxLength != 'undefined' && maxLength != null ) {
         if (limitExpression.length>0) limitExpression+=",";
         limitExpression += maxLength.toString();
       }

   return limitExpression.length>0?"{"+limitExpression+"}":"";
}

answered Sep 13, 2012 at 14:29

mplungjan

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