Why do these javascript regex throw syntax errors?

I am trying to validate a text string as a date before processing it, however both of the regex i have tried are throwing syntax errors and I can't see why. From what I can tell there is nothing wrong with either. These are the strings:

 var datePattern1 = new RegExp( (0[1-9]|1[012])[-](0[1-9]|[12][0-9]|3[01])[-](19|20)\d\d );

and

var datePattern2 = new RegExp( [0-3][0-9]-(0|1)[0-9]-(19|20)[0-9]{2} );

Appreciate any help.

From stackoverflow

• You are missing the quotes around your expressions:

  var datePattern1 = new RegExp( "(0[1-9]|1[012])[-](0[1-9]|[12][0-9]|3[01])[-](19|20)\d\d" );
  var datePattern2 = new RegExp( "[0-3][0-9]-(0|1)[0-9]-(19|20)[0-9]{2}" );
  

  MalcomTucker : is it really as simple as that? doh

  Guffa : No, it's not that simple. Also the \d\d at the end has to be \\d\\d.

• Either pass a string to the RegExp constructor as darin mentioned or use the RegExp syntax “/ … /”:

  var datePattern1 = /(0[1-9]|1[012])[-](0[1-9]|[12][0-9]|3[01])[-](19|20)\d\d/;
  var datePattern2 = /[0-3][0-9]-(0|1)[0-9]-(19|20)[0-9]{2}/;
  

• The Regexp() constructor expects a string, so you need to quote your regex:

  var datePattern2 = new RegExp('[0-3][0-9]-(0|1)[0-9]-(19|20)[0-9]{2}');
  

  When using double quotes, watch out for backslash escapes in the regex. Alternatively, you can use the Perl syntax:

  var datePattern2 = /[0-3][0-9]-(0|1)[0-9]-(19|20)[0-9]{2}/;
  

  MalcomTucker : if you use the perl syntax do you then pass the var to the regex constructor?

  Rob Kennedy : No. The slash syntax is a "regex literal." No need to create a Regex object around it.