Regex for number field

Question

I need a validate a textbox for numbers only alongwith a few special conditions. The allowed values are:

1. decimal numbers >= 0 [E.g. 25]
2. floating point numbers [E.g. 25.83]
3. decimal numbers with comma [E.g. 1,800]

I tried this regex method. but it is obviously not the correct regex for all the conditions. Please help in getting this fixed.

function validateText(text) { 
        var regex = new RegExp('^[0-9]+$');
        return regex.test(text);
    }