向对象添加方法

Question

我在javascript中向对象添加方法时遇到问题。 以下代码应返回一个数字，而是返回NaN。 希望你能帮忙

function people(name, age){
    this.name = name;
    this.age = age;
    this.numYearsLeft = pension();
}

function pension(){
    numYears = 65 - this.age;
    return numYears;
}

var andrews = new people("Andrews Green", 28);

console.log(andrews.numYearsLeft);

Answer 1

您可以使用原型模型 - 使pension成为people的方法 ：

function people(name, age){
  this.name = name;
  this.age = age;
  this.numYearsLeft = this.pension();  // note the `this`
}

people.prototype.pension = function(){ // note the `prototype`
  var numYears = 65 - this.age;
  return numYears;
};

var andrews = new people("Andrews Green", 28);

console.log(andrews.numYearsLeft);     // 37

使用prototype您的pension方法将继承构造函数（ people ）属性（允许您使用this关键字进行引用）。
这样做的另一个好处是，在每个new实例化people您都不会重新创建pension方法的新实例/召回。

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Introduction_to_Object-Oriented_JavaScript

Answer 2

JavaScript适用于“功能范围”，因此简而言之，你的范围是错误的。 您需要绑定“this”变量或使用prototype属性在people类上创建一个函数。

您可以将其定义为原型函数

people.prototype.pension = function() {
    numYears = 65 - this.age;
    return numYears;
}

Answer 3

如果在养老金中添加console.log（）行，您将看到this是窗口，而不是人员对象。 改变this情况的一种方法是使用call（）。

this.numYearsLeft = pension.call(this);

例：

 function people(name, age) { this.name = name; this.age = age; this.numYearsLeft = pension.call(this); } function pension() { numYears = 65 - this.age; return numYears; } var andrews = new people("Andrews Green", 28); console.log(andrews.numYearsLeft); 

其他选择是让它成为人原型的一部分。

 function people(name, age) { this.name = name; this.age = age; this.numYearsLeft = this.pension(); } people.prototype.pension = function () { numYears = 65 - this.age; return numYears; } var andrews = new people("Andrews Green", 28); console.log(andrews.numYearsLeft); 

Answer 4

为了调用函数，你需要put（）。 console.log(andrews.numYearsLeft); 应该是console.log(andrews.numYearsLeft());

也在

function pension(){
numYears = 65 - this.age;
return numYears;
}

this.age是未定义的，因此是NaN。

（已编辑）也许试试：

function people(name, age){
    var that = this;
    this.name = name;
    this.age = age;
    this.numYearsLeft = function(){
        numYears = 65 - that.age;
        return numYears;
    };
}
var andrews = new people("Andrews Green", 28);
console.log(andrews.numYearsLeft());