javascript - new Boolean(name) 始终返回 true

Question

这个问题已经有答案了:

Why does !new Boolean(false) equals false in JavaScript? (2 个回答)

已关闭 去年。

let name = window.prompt("Please Enter Your Name ");
let age = parseInt(window.prompt("Please Enter Your age "));

const nameCheck = new Boolean(name);
const ageCheck = new Boolean(age);

if ( nameCheck && ageCheck )
{
   console.log(`Hi ${name}, you were born in ${2020 - age}`)
}
else
{
   alert("You either entered no name, or your age was not a number");
}

即使我故意输入空字符串或年龄字母，if block 始终计算为 true 并执行。我认为空字符串在转换为 Boolean 时必须计算为 false ？

Answer 1

Boolean 并没有像你想象的那样做。它是一个对象，并且对象总是真实的:

> typeof new Boolean(false)
"object"
> if (new Boolean(false)) console.log("It's true!");
It's true!

要将值转换为原始 boolean 类型，常见的方法是将其取反两次:

const nameCheck = !!name;

您还可以将 Boolean 作为函数调用，但我会远离它，因为它不返回实际的 Boolean ，这相当令人困惑:

const nameCheck = Boolean(name);