javascript - 试图理解对象原型(prototype)

Question

为什么这段代码给我一个错误“Uncaught TypeError: Cannot set property 'grossSuperAnnuation' of undefined”？谢谢。

function taxCalculation(configuration){
      this.superAnnuationPercentage = configuration.superAnnuationPercentage;
      this.superAnnuationTaxRate    = configuration.superAnnuationTaxRate;
};

var tax = new taxCalculation({
    superAnnuationPercentage: 9.25,
    superAnnuationTaxRate:  15
});

tax.prototype.grossSuperAnnuation = function(income){
    return income * this.superAnnuationPercentage / 100;

};

Answer 1

您要更改的原型(prototype)是您的构造函数之一:

taxCalculation.prototype.grossSuperAnnuation = function(income){

如果你真的想从实例开始，你可以这样做:

tax.constructor.prototype.grossSuperAnnuation = function(income){

注意你可以做

tax.grossSuperAnnuation = function(income){

但是只有这个实例会具有该功能，而使用 new taxCalculation 创建的其他实例则不会。