var s = "xyz(0/0)"
var re = new RegExp("\((\\d+)\/(\\d+)\)","ig");
s = s.replace(re,function($0,$1,$2){return (parseInt($1)+1) + "/" + (parseInt($2)+2)});
alert(s);
var re = new RegExp("\((\\d+)\/(\\d+)\)","ig");
s = s.replace(re,function($0,$1,$2){return (parseInt($1)+1) + "/" + (parseInt($2)+2)});
alert(s);
var reg = /^(\w*\()(\d+)\/(\d+)\)$/g;
s = reg.exec(s);
alert(s[1]+(parseInt(s[2])+m)+'/'+(parseInt(s[3])+n)+')');
}<input type="text" onblur="repla('xyz(3/1)', 2, 2)">