如何从 JavaScript 中用作对象键的同名符号访问数据

Question

我正在学习 JavaScript 符号，根据我的阅读，它们用于保护对象属性键覆盖。在下面的代码中，我创建了两个具有相同变量名的符号并将它们用作对象键。我想知道如何访问分配给程序底部 "symbol" 键 之一的数据 。如果我完全误解了符号的用途，请指出。

var id = Symbol("my id");             // Create a Symbol

var user = {

    name:"Bob",
    age:30,
    [id]:"my id 12345"               // Use it as a property key and add some data
}

var id = Symbol("my different id"); // Create a new Symbol

user[id] = "my different id 9876"   // Assign it with some new data

console.log(user);

/* The object contains both symbols. No overwrites!


{

    name: "Bob", 
    age: 30, 
    Symbol(my id): "my id 12345", 
    Symbol(my different id): "my different id 9876"

}


*/

Answer 1

如果我没理解错的话，你需要

var id = Symbol.for("my id");

var user = {
    name:"Bob",
    age:30,
    [id]:"my id 12345"     
}

var id = Symbol.for("my different id");

user[id] = "my different id 9876"

console.log(user[Symbol.for("my id")]); 
console.log(user[Symbol.for("my different id")]);

id变量被重新赋值，所以你可以使用它只是为了获得"my different id 9876"符号不会被重新赋值。

Answer 2

I create two symbols of the same variable name and use them as object keys.

你为什么要这么做？ Symbols are meant to provide unique, non-enumerable property keys 以避免名称冲突。它们有两个不同的身份，应该用作常量，您可以从需要的地方引用它们。您甚至可以创建多个具有相同描述的不同符号：

const idA = Symbol("my id");
const idB = Symbol("my id");
console.log({[idA]: 12345, [idB]: 9876});

I want to know how to access the data assigned to either one of the "symbol" keys at the bottom of the program.

只保留对它们的引用：

const myId = Symbol("my id");
const myDifferentId = Symbol("my different id");

var user = {
    name:"Bob",
    age:30,
    [myId]:"my id 12345"
};
user[myDifferentId] = "my different id 9876";

console.log(user);
console.log(user[myId], user[myDifferentId]);

如果您没有保留参考，您也可以使用 Object.getOwnPropertySymbols function.

访问它们

如何从 JavaScript 中用作对象键的同名符号访问数据

How to access data from same name Symbols used as object keys in JavaScript

javascript

symbols

ecmascript-6