String.replace method in javascript using regex -

I came to this example using strings on the replacement method.

This example is quoted there

  var again = / (\ w +) \ s (\ w +) /; Var str = "John Smith"; Var newstr = str.replace (again, "$ 2, $ 1"); Print (newstr); // Smith, John   
 I changed regex into the following and tested it.  
  var re = / (\ w?) (\ W +) /; Var str = "John Smith"; Var newstr = str.replace (again, "$ 1, $ 1"); Newstr; // J, Oh Smith var newstr1 = str.replace (again, "$ 2, $ 1"); Newstr1; // Oh, J Smith should be $ 1  J  and $ 2 should be  ohn smith  in this example When I reverse the order of newstr1 for $ 1, then it should be 'Ohhan Smith, J' but it's not.  
 What is my understanding of $ 1 and $ 2 (substring matching is correct) and why is newstr1 different?  
 Thanks for the comments   ,  $ 1  is  "J" ,  $ 2 < / Code> 
 
  "ohn"  and  "smith"  is unrivaled.  
  var re = / (\ w?) (\ W +) /, Str = "John Smith"; ('$ 1', $ 1); Console.log ('$ 2', $ 2); Return ''; // Simply leave unmatched}); / * Match John $ 1 J $ 2 Ohanna "Smith" * /   
 Therefore, your swap with  j  with  oh  Switching, give you  newstr1 .  
  Why is this happening?  Because  \ w  matches  , but ?  makes this optional, so as in  (. *?) (.) Captures one letter in   $ 1 ,  (\ W?)  is doing the second capture,  (\ w +)  can only extend to the end of the word, despite  + , because  \ W  does not match whitepaper  \ s .