Check if a string contains brackets with an integer in it

I want to check if a string in javascript contains regular brackets with an integer in it

var str="(12) this is a test";
var pat=/(([\d]+))/;
if (pat.test(str)) 
    alert("true");

      

        
        
        
      

    

Works fine, but also returns true when the string looks like this:

var str="12) test";
var str="(12 test";

      

        
        
        
      

    

which should return false.