var test = [
    'Mercu"ry', 'Mercu,ry', 'Mer"cu,ry', 'Mercury'
];


for (x in test) {
    var s = test[x];
    if (s.indexOf('"') != -1) {
        s = s.replace(/"/g, '""');
    }

    if (s.match(/"|,/)) {
        s = '"' + s + '"';
    }

    alert(s);
}

Test: http://jsfiddle.net/ZGFV5/

Try to run the code with Mer""cury :)

I tried it just for fun, even though it is certainly better to fix the generator. This might work in your case, or at least inspire you:

You can try it here

$( function() 
{
  var myString = "{ \"na\"\"me\": \"va\"lue\", \"tes\"\"t\":\"ok\" }";
  var myRegexp = /\s*\"([\w\"]+)\"\s*[,}:]/g;
  var match;
  var matches = [];

  // Save all the matches
  while((match = myRegexp.exec(myString)) !== null)
  {
      matches.push(match[1]);
      console.log(match[1]);
  }

  // Process them
  var newString = myString;
  for (var i=0; i<matches.length; i++)
  {
      var newVal = matches[i].replace(/\"/g, '\\\"'); 
      newString = newString.replace(matches[i], newVal);
  }
  alert(myString + "\n" + newString);
}
);

You need to use a global regular expression for this. Try it this way:

str.replace(/"/g, '\\"');

Check out regex syntax and options for the replace function in Using Regular Expressions with JavaScript.

This would be possible with the help of positive lookahead assertion.

var s = '{"place": {"address": "Main Street, "The House""}}';
alert(s.replace(/"((?:"[^"]*"|[^"])*?)"(?=[:}])/g, function(m,group)
                          {
                            return '"' + group.replace(/"/g, '\\"') + '"'
                          }))

OR

var s = '{"place": {"address": "Main Street, "The House"", "country": "United Kingdom"}}';
alert(s.replace(/"((?:"[^"]*"|[^"])*?)"(?=[:},])(?=(?:"[^"]*"|[^"])*$)/gm, function(m,group)
                          {
                            return '"' + group.replace(/"/g, '\\"') + '"'
                          }))

The thing is that .replace() does not modify the string itself, so you should write something like:

strInputString = strInputString.replace(...

It also seems like you're not doing character escaping correctly. The following worked for me:

strInputString = strInputString.replace(/'/g, "\\'");

You will need to use regular expression for this,

st.replace(/"/g, '\\"');

Check out more on regular expressions here.

It should be:

var str='[{"Company": "XYZ","Description": "\\"TEST\\""}]';

First, I changed the outer quotes to single quotes, so they won't conflict with the inner quotes. Then I put backslash before the innermost quotes around TEST, to escape them. And I escaped the backslash so that it will be treated literally.

You can get the same result with use of a JSON function:

var str=JSON.stringify({Company: "XYZ", Description: '"TEST"'});