javascript - 在正则表达式中使用变量

Question

我正在尝试从中Smith提取name到lastName.

function reggie(){
  var name = "JohnSmith";
  var first = "John";
  var regExp = new RegExp("(?:"+first+")(w+)", "gi");
  var lastName = regExp.exec(name);
  //Logger.log(lastName); // in google apps
  console.log(lastName);
}
reggie()