javascript - 从类构造函数中的另一个属性引用属性的值

Question

我试图从另一个属性中的另一个方法引用属性中先前方法返回的值
在构造函数中，但我收到“TypeError:无法读取未定义的属性'名称'”

class Loans {
  constructor(user, loanAmount, tenor, id = 0, status = 'pending', repaid = 'false') {
    this.id = id + 1;
    this.user = user;
    this.loanAmount = loanAmount;
    this.tenor = tenor;
    this.status = status;
    this.repaid = repaid;
    this.interest = (function interest() {
      return (loanAmount * 0.05);
    }());
    this.monthlyInstall = (function monthlyInstall() {
      return (loanAmount + this.interest) / tenor;
    }());
    this.balance = (function balance() {
      return (loanAmount + interest);
    }());
    this.createdAt = new Date().toLocaleString();
  };

};
const loan = new Loans('steve.jobs', 50000, 5);
console.log(loan);

but I got an error ->

      return (loanAmount + this.interest) / tenor;
                                ^

TypeError: Cannot read property 'interest' of undefined
    at monthlyInstall (C:\Users\DEBAYO\Desktop\JavaScript\Challenges\testing.js:183:33)
    at new Loans (C:\Users\DEBAYO\Desktop\JavaScript\Challenges\testing.js:184:6)

Answer 1

如果您希望此金额是动态的(您更新他们相应更新的值)，它们需要是函数。我在下面为它们定义了函数。这意味着如果您更改其中一个计算变量，它们将自动更新。

class Loans {
  constructor(user, loanAmount, tenor, id = 0, status = 'pending', repaid = 'false') {
    this.id = id + 1;
    this.user = user;
    this.loanAmount = loanAmount;
    this.tenor = tenor;
    this.status = status;
    this.repaid = repaid;
    this.createdAt = new Date().toLocaleString();
  };
  
  interest = () => (this.loanAmount * 0.05);
  monthlyInstall = () => (this.loanAmount + this.interest()) / this.tenor;
  balance = () => (this.loanAmount + this.interest());
};
const loan = new Loans('steve.jobs', 50000, 5);
console.log(loan);
console.log(loan.interest());
console.log(loan.monthlyInstall());
console.log(loan.balance());
loan.tenor = 6;
console.log(loan);
console.log(loan.interest());
console.log(loan.monthlyInstall());
console.log(loan.balance());