javascript - js中的this关键字

Question

您好，我正在编写一个简单的模块函数来计算餐馆账单，但我的总金额没有相加，我假设这是因为 this 关键字

//Function meant to be used as a constructor
var Calculator = function(aPercentage){ 
  this.taxRate  = aPercentage;
  this.tipRate = aPercentage;
}
Calculator.prototype.calcTax = 
  function(amount) {return amount*(this.taxRate)/100;}
Calculator.prototype.calcTips =
  function(amount)  {return amount *(this.tipRate)/100;}
Calculator.prototype.calcTotal = 
  function(amount) {return (amount + (this.calcTips(amount) )+ this.calcTax(amount));}

module.exports = Calculator;

//This the code that calls the calculator
var Calculator = require("./Calculator.js");

var taxCalculator  = new Calculator(13); //13% Ontario HST
var tipsCalculator = new Calculator(10); //10% tips

var itemPrice = 200; //$200.00

console.log("price: $" + itemPrice);
console.log("tax:   $" + taxCalculator.calcTax(itemPrice));
console.log("tip:   $" + tipsCalculator.calcTips(itemPrice));
console.log("---------------");
console.log("total: $" + taxCalculator.calcTotal(itemPrice));

我应该得到的总价是:itemPrice + 税 + 小费 = 200+26+20 = 246 但我一直得到 252 这意味着我得到 200+ 26+26，这是没有意义的。谁能详细说明一下吗？

Answer 1

您需要在同一个构造函数中传递两个值，如下所示

function Calculator (taxPercentage, tipPercentage) { 
    this.taxRate = taxPercentage;
    this.tipRate = tipPercentage;
}

你会创建一个像这样的对象

var billCalculator = new Calculator(13, 10);

并调用这样的函数

console.log(billCalculator.calcTax(200));
// 20
console.log(billCalculator.calcTips(200));
// 26
console.log(billCalculator.calcTotal(200));
// 246