javascript - 在 JavaScript 中更改元数据是如何工作的？

Question

在控制台中，我得到 abc尽管设置 {writable:false} .您能解释一下更改元数据的工作原理吗？

let portfolio = {
  myFirstName: "Bob",
  myLastName: "Alice",
  myAge: 26,
  aboutMe: function() {
    return ("First Name: " + this.myFirstName + "; Last Name: " + this.myLastName + "; Age: " + this.myAge + ";");
  }
};
Object.defineProperty(portfolio, "myFirstName", { writable: false });
Object.defineProperty(portfolio, "myFirstName", { value: "abc" });
console.log(portfolio.myFirstName);

Answer 1

在你的第二行 Object.defineProperty(portfolio, "myFirstName", { value: "abc" });您正在再次定义该属性。
您没有分配值。您正在扔掉旧房产并用全新的品牌取而代之。 (技术上不正确，它经历了很多步骤到 evaluate and apply values to property properties ，但为了简单理解，我相信这足以理解，因为在这种情况下感觉像是一个新的。如果你想拥有复杂的，请阅读链接真相)
要分配新值，请使用 portfolio.myFirstName = "value here"你会看到它被写保护了。

let portfolio = {
  myFirstName: "Bob",
  myLastName: "Alice",
  myAge: 26,
  aboutMe: function() {
    return ("First Name: " + this.myFirstName + "; Last Name: " + this.myLastName + "; Age: " + this.myAge + ";");
  }
};
Object.defineProperty(portfolio, "myFirstName", { writable: false });
portfolio.myFirstName = "Alice";
console.log(portfolio.myFirstName);

为防止出现这种变通方法，请调用 Object.freeze()修改其属性后在对象上。这也会产生其他副作用，例如无法编辑其他属性的值。

let portfolio = {
  myFirstName: "Bob",
  myLastName: "Alice",
  myAge: 26,
  aboutMe: function() {
    return ("First Name: " + this.myFirstName + "; Last Name: " + this.myLastName + "; Age: " + this.myAge + ";");
  }
};
Object.defineProperty(portfolio, "myFirstName", { writable: false });
Object.freeze(portfolio);
Object.defineProperty(portfolio, "myFirstName", {value:"abc"});
console.log(portfolio.myFirstName);