符号:隐式字符串转换在JavaScript中如何工作? [英] Symbols: How does implicit string conversion work in JavaScript?

问题描述

阅读JavaScript中Symbol的文档，并在一些环境(Chrome，Firefox，Node.js)中进行测试，我意识到我对隐式字符串转换的理解是有缺陷的.

Reading the documentation on Symbols in JavaScript, and also testing in a few environments (Chrome, Firefox, Node.js), I've realized that my understanding of implicit string conversion is flawed.

我总是给人一种印象，尝试转换为字符串时会调用对象的toString()方法，如果该函数未返回原语，则它将调用对象的toPrimitive()方法，如果不起作用，它将输入错误.但是，此说明未能涵盖Symbol抛出的TypeError:

I was always under the impression that the object's toString() method was called when attempting to convert to a string, and if that function didn't return a primitive, then it called the object's toPrimitive() method, then if that didn't work it would type-error. However, this explanation fails to cover the TypeError that Symbols throw:

var sym = Symbol("test");

try {
  console.log(sym + "ing");
} catch (error) {
  console.error(error);
}

TypeError: Cannot convert a Symbol value to a string

但是很明显Symbol具有有效的toString()方法.那么为什么不叫它呢?

But it's apparent that Symbols have a valid toString() method. So why isn't it called?

推荐答案

您正确的是，在进行隐式字符串转换时将调用对象toString方法.但是，如规范所述，符号上的隐式字符串转换会导致TypeError

You're right that an objects toString method is called when doing implicit string conversions. However, as the spec states, implicit string conversions on symbols cause a TypeError.

如博士. Axel Rauschmayer说了:

鉴于字符串和符号都可以是属性键，因此您希望保护人们免于意外将符号转换为字符串.

Given that both strings and symbols can be property keys, you want to protect people from accidentally converting a symbol to a string.

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