javascript - Setter 和 Getter 错误

Question

function Point () {
    this.xPos = 0;
    this.yPos = 0;
}

Object.__defineGetter__.call(Point.prototype, "getPoint", function(){
    return "X: " + this.xPos + " Y: " + this.yPos;
});

Object.__defineSetter__.call(Point.prototype, "setPoint", function(point){
    var parts = point.toString().split(', ');
    parts[0] = this.xPos;
    parts[1] = this.yPos;
});

var newPoint = new Point();

newPoint.setPoint("44.5, 60.6");

console.log(newPoint.getPoint);

它返回一个错误:newPoint.setPoint 不是一个函数。不明白为什么你能帮助我？尝试处理 setter 和 getter。

Answer 1

您遇到的主要问题是通过使用赋值运算符 = 来调用 setter。

newPoint.setPoint = "44.5, 60.6";

function Point () {
    this.xPos = 0;
    this.yPos = 0;
}

Object.__defineGetter__.call(Point.prototype, "getPoint", function(){
    return "X: " + this.xPos + " Y: " + this.yPos;
});

Object.__defineSetter__.call(Point.prototype, "setPoint", function(point){
    var parts = point.toString().split(', ');
    // the assignment to this.xPos and this.yPos was the wrong way around
    this.xPos = parts[0];
    this.yPos = parts[1];
});

var newPoint = new Point();

// a setter is called by assigning a value to it
newPoint.setPoint = "44.5, 60.6";

console.log(newPoint.getPoint);

您还可以使用 Object.defineProperty 或 Object.defineProperties 的标准 API，这对于查看代码的其他人来说更容易理解。

Object.defineProperty(Point.prototype, "getPoint", {
  get: function(){
    return "X: " + this.xPos + " Y: " + this.yPos;
  },
  set: function() {
    // stuff
  }
});

或者使用 ES6

class Point {
  constructor() {
     this.xPos = 0
     this.yPos = 0
  }
  get getPoint() {
      // stuff
  }
  set setPoint() {
     // stuff
  }
}