Javascript String interpolate(o)

String.prototype.interpolate = function (o) {
  return this.replace(/%\{([^\{\}]*)\}/g, function (a, b) {
      var r = o[b];
      return typeof r === 'string' || typeof r === 'number' ? r : a;
    }// w  w  w  . jav a2s. co  m
  );
};