本文介绍了使用||的代码的确切含​​义是什么? (“OR”)运算符?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!

问题描述

我在某处看到了这段代码:

I saw somewhere this code snippet:

var idx = SOME_VALUE;

var color = {
  yellor: 1,
  red: 2,
  black: 0
};

var x = color[idx] || []; // Is this means if color[idx] is null, then return an empty array?

我只能猜测代码 var x = color [idx] || []; 表示如果 color [idx] 为null,则返回一个空数组为x,否则为x = color [idx]。我是对的吗?

I can only guess the code var x = color[idx] || []; means if color[idx] is null, then return an empty array to x otherwise x= color[idx]. Am I right?

不过,我需要一个解释。此代码是否具有与以下相同的逻辑?

Still, I need an explaination. Does this code has the same logic as the following?

CONDITION==VALUE? TRUE_goes_here : FALSE_goes_here


推荐答案

这意味着如果 color [idx] 是falsy,而是使用空数组。 Falsy值 false (当然), 0 NaN undefined null (所有其他值都是真实的)。这个成语是JavaScript的一个例子 *。

What it means is that if color[idx] is "falsy," use an empty array instead. "Falsy" values are false (of course), 0, NaN, "", undefined, and null (all other values are "truthy"). That idiom is an example of JavaScript's curiously powerful || operator*.

在这种情况下,如果 color 不包含名称包含在 idx 中的属性(因为当您索引这样的对象并且密钥与任何现有密钥不匹配时属性名称,结果是 undefined ): x 1 (如果 idx 是yellor), 2 (如果 idx 是红色), 0 (如果 idx 是黑色),或 [] 如果 idx 是其他任何内容。

In this case, it's supplying a default value if color doesn't contain a property with the name contained by idx (because when you index into an object like that and the key doesn't match any existing property name, the result is undefined): x will be 1 (if idx is "yellor"), 2 (if idx is "red"), 0 (if idx is "black"), or [] if idx is anything else.

所以回答你的问题在你的问题的最后,基本上,是的。它是:

So answering your question at the end of your question, basically, yes. It's:

var x = color[idx];
if (!x) {
    x = [];
}

var x = color[idx] ? color[idx] : [];






* (这是我的帖子)贫穷的小博客。)

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10-21 02:07