ES6：WeakSet 上的 console.log 给出<item unknown></item>

Question

为什么console.log将 WeakSet 显示为<items unknown> ？

[13:37:11] [~] node
Welcome to Node.js v14.4.0.
Type ".help" for more information.
> let student1 = { name: 'James', age: 26 };
undefined
> let student2 = { name: 'Julia', age: 27 };
undefined
> const roster = new WeakSet([student1, student2]);
undefined
> console.log(roster);
WeakSet { <items unknown> }
undefined

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上下文：我在 ES6 中的WeakSet上遇到了以下示例。

let student1 = { name: 'James', age: 26 };
let student2 = { name: 'Julia', age: 27 };
const roster = new WeakSet([student1, student2]);
console.log(roster);

该示例表明它应该打印

WeakSet {Object {name: 'Julia', age: 27}, Object {name: 'Richard', age: 31}}

但在节点 v14.4.0 中，它会打印

WeakSet { <items unknown> }

Answer 1

node-js 团队认为很难正确实现它。 这是问题： https://github.com/nodejs/node/issues/19001

所以这意味着 WeakSet 可以正常工作但 console.log 将始终 output 为空的 WeakSet

如果您仍想检查 WeakMap，您可以使用 utils inspect 来做到这一点：

const { inspect } = require('util');
let student1 = { name: 'James', age: 26 };
let student2 = { name: 'Julia', age: 27 };
const weakSet = new WeakSet([student1, student2]);
console.log(inspect(weakSet, { showHidden: true }));