Javascript regex replace is not working sometimes -

i using regex search words same , replace same ones. replaced word changes original word time time. i'm not sure why.

here code.

function censor(word, string){      var newstring = '';    var replacestring = '';    var rand = math.floor(math.random() * 10) + 1;      for(var x = 0 ; x < word.length ; x++){      switch (rand) {        case 1:          replacestring += '!';          break;        case 2:          replacestring += '@';          break;        case 3:          replacestring += '#';          break;        case 4:          replacestring += '$';          break;        case 5:          replacestring += '%';          break;        case 6:          replacestring += '^';          break;        case 7:          replacestring += '&';          break;        case 8:          replacestring += '*';          break;        case 9:          replacestring += '(';          break;        case 10:          replacestring += ')';          break;      }      var rand = math.floor(math.random() * 10) + 1;    }      newstring = string.replace(new regexp(word,'g'), replacestring);    return newstring;    }    var string = censor('damn', 'omg damn smart, damn !');  console.log(string);

here of results unexpected.

• omg @%damn smart, @%damn !
• omg damn&& smart, damn&& !

there few sequences in replacement string expanded:

• $&, entire match
• $`, string before match
• $', string after match
• $d (d digit), captured group @ index
• $$, single $

your random generator producing $& (and possibly $$). change

replacestring += '$'; 

to

replacestring += '$$'; 

and things should work properly.