Question

Is that possible to pass variable into regular expression pattern string in jquery ( or javascript)? For example, I want to validate a zip code input field every time while user type in a character by passing variable i to the regular expression pattern. How to do it right?

 $('#zip').keyup( function(){ 
 var  i=$('#zip').val().length
 for ( i; i<=5; i++){   
            var pattern=/^[0-9]{i}$/;  
     if ( !pattern.test(   $('#zip').val()   )    )
                {$('#zip_error').css('display','inline');}   
     else
         {$('#zip_error').css('display','none');}
   }
 })

Answer 1

Yes, you can, using the RegExp constructor:

var pattern = new RegExp("^[0-9]{"+i+"}$");

But… looking at your code seems that you want to ensure that the textbox contains only numbers, for that you can use a simple regex like this:

var pattern = /^[0-9]+$/;

The above pattern will only match a string composed by numbers, it will look for:

• Beginning of a line ^
• Match a single digit character [0-9]
  • Between one and unlimited times +
• End of line $