向對象添加方法

Question

我在javascript中向對象添加方法時遇到問題。 以下代碼應返回一個數字，而是返回NaN。 希望你能幫忙

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成為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方法將繼承構造函數（ people ）屬性（允許您使用this關鍵字進行引用）。
這樣做的另一個好處是，在每個new實例化people您都不會重新創建pension方法的新實例/召回。

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

Answer 2

JavaScript適用於“功能范圍”，因此簡而言之，你的范圍是錯誤的。 您需要綁定“this”變量或使用prototype屬性在people類上創建一個函數。

您可以將其定義為原型函數

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

Answer 3

如果在養老金中添加console.log（）行，您將看到this是窗口，而不是人員對象。 改變this情況的一種方法是使用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); 

其他選擇是讓它成為人原型的一部分。

 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

為了調用函數，你需要put（）。 console.log(andrews.numYearsLeft); 應該是console.log(andrews.numYearsLeft());

也在

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

this.age是未定義的，因此是NaN。

（已編輯）也許試試：

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());