如何获得符号属性的值 [英] How can I get the value of a Symbol property

问题描述

我在NodeJS中有一个对象（准确地说是一个套接字）。

打印时，我看到其中一项是这样的：

  [Symbol（asyncId）]：2781 //数值更改
  

如何获取此类密钥的值？

我尝试过 socket ['[Symbol（asyncId）]'] ，但未定义 。

表达式 socket。[Symbol（asyncId）] 显然不起作用。

解决方案

您将无法直接通过键访问它，除非您引用了实际值： Symbol（'asyncId'），因为每个符号都是唯一

Symbol（）函数返回一个symbol类型的值，具有静态的
属性，该属性公开多个成员的内置对象，具有公开全局符号注册表的静态
方法，并且类似于
内置对象类，但不完整作为构造函数，因为
不支持语法 new Symbol（）。

您可以做的是循环通过使用反射来访问对象自身的属性键。 ownKeys ，其中将包含普通属性&符号，然后获取该引用。

您还可以使用： Object.getOwnPropertySymbols（）

  function getObject（）{//在此范围之外，您无权访问此符号。 const symbol = Symbol（'asyncId'）; return {foo：‘bar’，[symbol]：42};} const obj = getObject（）; console.log（obj）; console.log（obj [Symbol（’asyncId'）]））; // undefined //或Object.getOwnPropertySymbols（obj）const symbolKey = Reflect.ownKeys（obj）.find（key => key.toString（）==='Symbol（asyncId）'）console.log（obj [symbolKey ]）; // 42  

注意：对象可以有多个键，其中 key.toString（）==='Symbol（asyncId）'，这不是很常见，但是请注意，因此您可能想要可以使用 .find 以外的其他功能。

注意II ：
不应更改该属性的值，因为它应该仅用于内部访问，即使该属性不是只读的。

< pre class = snippet-code-js lang-js prettyprint-override> function getObject（）{//在此范围之外，您无权访问此符号。 const symbol = Symbol（'asyncId'）; const symbol2 = Symbol（'asyncId'）; return {foo：'bar'，[symbol]：'我不需要的值'，[symbol2]：'我想要的值'};} const obj = getObject（）; const symbolKey = Reflect.ownKeys （obj）.find（key => key.toString（）==='Symbol（asyncId）'）console.log（obj [symbolKey]）; //我不需要的值console.log（'===所有值==='）; Reflect.ownKeys（obj）.forEach（key => console.log（obj [key]））;

I have an object in NodeJS (a socket to be accurate).

When I print it, I see that one of the entries is this:

[Symbol(asyncId)]: 2781 // the numeric value changes

How can I obtain the value of such key?

I've tried socket['[Symbol(asyncId)]'] but got undefined.

The expression socket.[Symbol(asyncId)] would obviously not work.

解决方案

You will not be able to access it directly by key, unless you have a reference to the actual: Symbol('asyncId'), because every Symbol is unique

The Symbol() function returns a value of type symbol, has static properties that expose several members of built-in objects, has static methods that expose the global symbol registry, and resembles a built-in object class but is incomplete as a constructor because it does not support the syntax "new Symbol()".

What you can do is loop through the object's own property keys, using Reflect.ownKeys, which will include normal properties & symbols, and then obtain that reference.

You can also use: Object.getOwnPropertySymbols()

function getObject() {
   // You don't have access to this symbol, outside of this scope.
  const symbol = Symbol('asyncId');

  return {
    foo: 'bar',
    [symbol]: 42
  };

}

const obj = getObject();

console.log(obj);
console.log(obj[Symbol('asyncId')]); // undefined

// or Object.getOwnPropertySymbols(obj)
const symbolKey = Reflect.ownKeys(obj)
  .find(key => key.toString() === 'Symbol(asyncId)')
  
console.log(obj[symbolKey]); // 42
 

NOTE: The object can have multiple keys where key.toString() === 'Symbol(asyncId)', this won't be usual, but be aware, so you may want to use other function other than .find if that's the case.

NOTE II: You should not change the value of that property, since it's supposed to be for internal access only, even if the property is not read only.

function getObject() {
       // You don't have access to this symbol, outside of this scope.
      const symbol = Symbol('asyncId');
      const symbol2 = Symbol('asyncId');

      return {
        foo: 'bar',
        [symbol]: 'the value I don\'t want',
        [symbol2]: 'the value I want'
      };

}
const obj = getObject();

const symbolKey = Reflect.ownKeys(obj)
  .find(key => key.toString() === 'Symbol(asyncId)')
  
console.log(obj[symbolKey]); // the value I don't want

console.log('=== All values ===');
Reflect.ownKeys(obj)
  .forEach(key => console.log(obj[key]));

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