构造函数的JavaScript输出返回为'undefined'

Question

当我将参数传递到console.log()内的undefined时，结果会回来var Bike = function() { var gear = 2; // private var set to an arbitrary number this.setGear = function(change) { // public method gear = change; }; this.getGear = function() { // public method return gear; }; }; var myBike = new Bike(); console.log(myBike.setGear(4)); // returns undefined, should return 4 console.log(myBike.setGear(3)); // returns undefined, should return 3 console.log(myBike.setGear(1)); // returns undefined, should return 1 ，为什么会这样？结果应该是我传入的数字。

{{1}}

Answer 1

this.setGear = function(change) { // public method
  gear = change;
};

不应该返回4.

this.setGear = function(change) { // public method
  gear = change;
  return gear;
};

应该

Answer 2

如果你设置myBike.setGear，你应该调用myBike.getGear函数来返回齿轮; myBike.setGear(4); console.log(myBike.getGear);