Question

如何将变量 balance 设为私有，同时在文本字段中保留值100.00？

HTML文本字段：

<span type="text" id="txtMyAccountBalance">&nbsp;</span>

功能如下：

function TAccount()
  {
      this.balance = 0.0;
      this.printOut = function () {
          txtMyAccountBalance.innerText = this.balance.toFixed(2);
      }
  }

var currentAccount = new TAccount ();

currentAccount.balance = 100.0;

这很好用，文本字段显示余额为100.00。如何将变量 balance 设为私有？我想我必须使用 var 而不是 this ，但是如何？

Answer 1

在这种情况下，实际上您确实可以使用var！

function TAccount() {
  var balance = 0.0; // This is not accessible outside of this function, making it practically "private"

  this.printOut = function () {
    // It feels a bit weird, but here we "just" use the balance variable that is defined outside this function
    txtMyAccountBalance.innerText = balance.toFixed(2);
  }

  this.doubleBalance = function() {
    // Same way we can change it by re-assigning
    balance = balance * 2;
  }
}

请不要将此用于安全性，因为它不安全。人们仍然可以进入javascript控制台并侵入代码中，以将其设置为不同的值。不可能由用户操纵的值是不可能的！

Answer 2

您可以使用Symbol语法

var TAccount = (function() {

    var balanceSymbol = Symbol('balance');

    TAccount.prototype.setBalance = function(BAL) {
        this[balanceSymbol] = BAL;
    }

    TAccount.prototype.getBalance = function() {
        return this[balanceSymbol];
    }

    TAccount.prototype.printOut = function () {
        txtMyAccountBalance.innerText = this.balance.toFixed(2);
    }


});

var currentAccount = new TAccount();

currentAccount.setBalance(100.0);
console.log(currentAccount.balance); // undefined
console.log(currentAccount.getBlance()); // 100

如何将变量设为私有？

2 个答案: