内置对象包装器(使用 Boolean、Number、String 和 Date 构造函数)将原始包装值存储在名为 [[PrimitiveValue]] 的内部属性中，该属性无法更改，但是...

Built-in object wrappers (created with the Boolean, Number, String and Date constuctors) store the primitive wrapped value in an internal property named [[PrimitiveValue]], which cannot be changed, but...

您可以覆盖 test 对象的 valueOf 方法:

You can override the valueOf method of your test object:

var test = new Boolean(0);
test.prop = "OK!"
// override valueOf:
test.valueOf = function () { return true; };

if (test == true) { // using the equals operator explicitly for type conversion
  alert(test.prop); //"OK!"
}

它会起作用，因为 valueOf 方法是由 equals 运算符触发的类型转换机制在内部使用的.

It will work since the valueOf method is used internally by the type-conversion mechanisms triggered by the equals operator.

当其中一个操作数是布尔值时，两者都在末尾转换为数字.

When one of the operands is a Boolean value, both are converted at the end to Number.

如果我们不使用等号运算符(例如 if (test) { ... })，因为 test 是一个对象，当直接转换为 Boolean，它总是会产生 true.

If we don't use the equals operator (e.g. if (test) { ... }), since test is an object, when converted directly to Boolean, it will always yield true.

任何转换为​​布尔值的对象都会产生 true 值，唯一可以产生 false 结果的值是falsey"值(null、undefined、0、NaN，一个空字符串，当然还有false值)，其他任何事情都会产生 true.

Any object converted to Boolean will produce the true value, the only values that can produce a false result, are the "falsey" values (null, undefined, 0, NaN, an empty string, and of course the false value), anything else will produce true.

更多信息:

• 对象到原始的转换