Replace all the dots in a number

I'm trying to replace all dots found in a value entered by the user in an HTML form. For instance I need the entry '8.30' to be converted to '8x30'.

I have this simple code:

var value = $(this).val().trim(); // get the value from the form
value += ''; // force value to string
value.replace('.', 'x');

But it doesn't work. Using the console.log command in Firebug, I can see that the replace command simply does not occur. '8.30' remains the same.

I also tried the following regexp with no better result:

value.replace(/\./g, 'x');

What am I doing wrong here?