replace all occurance of particular portion

function replace(string,text,by) {
// Replaces text with by in string
var strLength = string.length, txtLength = text.length;
if ((strLength == 0) || (txtLength == 0)) return string;

var i = string.indexOf(text);
if ((!i) && (text != string.substring(0,txtLength))) return string;
if (i == -1) return string;

var newstr = string.substring(0,i) + by;

if (i+txtLength < strLength)
newstr += replace(string.substring(i+txtLength,strLength),text,by);

return newstr;
}