在JavaScript中将值转换为字符串

Converting values to strings in JavaScript is more complicated than it might seem:

在 JavaScript 中将值转换为字符串比看起来要复杂：

• Most approaches have values they can’t handle.
• 大多数方法都有无法处理的值。
• We don’t always see all of the data.
• 我们并不总是能看到所有数据。

Converting values to strings  #

将值转换为字符串  #

Example: code that is problematic  #

示例：有问题的代码  #

Can you spot the problem in the following code?

你能在以下代码中发现问题吗？

class UnexpectedValueError extends Error { constructor(value) { super('Unexpected value: ' + value); 
  }
}

For some values, this code throws an exception in line A:

对于某些值，这段代码在 A 行抛出异常：

 new UnexpectedValueError(Symbol())
TypeError: Cannot convert a Symbol value to a string new UnexpectedValueError({__proto__:null})
TypeError: Cannot convert object to primitive value

Read on for more information.

继续阅读以获取更多信息。

Five ways of converting values to strings  #

将值转换为字符串的五种方法  #

These are five common ways of converting a value v to string:

这五种将值 v 转换为字符串的常见方法：

• String(v)
• String(v)
• '' + v
• '' + v
• `${v}`
• `${v}`
• v.toString()
• v.toString()
• {}.toString.call(v)
• {}.toString.call(v)

Which of these should we use? Let’s first check how they fare with the following tricky values:

我们应该使用哪一个？让我们先检查它们在以下棘手值上的表现：

• undefined
• undefined
• null
• null
• Symbol()
• Symbol()
• {__proto__: null}
• {__proto__: null}

These are the results:

这些是结果：

Conclusions:

结论：

• Among the five approaches listed in the table only {}.toString.call(v) works for all tricky values.
• 在表中列出的五种方法中，只有 {}.toString.call(v) 对所有棘手的值都有效。
• If we don’t need to be 100% safe and would like to be less verbose then String(v) is also a good solution.
• 如果我们不需要 100% 安...