Javascript：空对象是假的吗？ [英] Javascript: Is an empty object a falsy one?

问题描述

空对象未定义，如此var empty_obj = {}。
未定义的将是假的。但我注意到
empty_obj || 3将返回empty_obj而不是3.
为什么？

The empty object is undefined, like this var empty_obj = {}. An undefined will be a false one. But I notice that empty_obj || 3 will return the empty_obj not 3. Why is that?

推荐答案

空对象不 undefined。

The empty object is not undefined.

console.log({} === undefined); // false
console.log(typeof {}); // object

这是一个真正的价值：

if ({}) console.log('truthy'); // truthy

它甚至有一些属性：

console.log(typeof {}.hasOwnProperty); // function

JS中唯一的假值是 0 ， false ， null ， undefined ，空字符串， NaN 。

The only falsy values in JS are 0, false, null, undefined, empty string, and NaN.

您可能会对此感到困惑返回值 var = 语句。这些将始终在Chrome控制台中显示为 undefined ：

You may be confused by the return value of var = statements. These will always show as undefined in the Chrome console:

> var obj = {}
undefined
> var x = 100
undefined
> var y = "potato"
undefined

仅仅因为 var = 语句返回undefined并不意味着该值未定义。虽然，如果没有 var ，分配会返回分配的值：

Just because the var = statement returns undefined doesn't mean the value was undefined. Although, without the var, assignments do return the value being assigned:

> obj = {}
{}
> x = 100
100
> y = "potato"
"potato"

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