`var options = options ||之间的区别{}`和`选项|| （options = {}）` [英] Difference between `var options = options || {}` and `options || (options = {})`

问题描述

我经常使用 var options = options || {} 作为默认为空对象的方法。它通常用于初始化一个选项对象，以防它未在函数调用的参数中传递。

I often use var options = options || {} as way to default to an empty object. It's often used to initialize an option object in case it's not passed in the parameter of a function call.

我在几个地方读过的东西（博客帖子，源代码）选项|| （options = {}）更好地表达开发人员的意图。有人可以详细说明吗？我没有看到两者之间的功能差异，所以我必须在这里找到一些东西。

The thing is I've read in several places (blog posts, source code) that options || (options = {}) better express the developer's intent. Can someone elaborate on it? I don't see the functional difference between the two, so there's something I must be missing here.

---编辑

我在几个地方的Backbone.js源代码中看到过，比如 https://github.com/documentcloud/backbone/blob/0.9.2/backbone.js#L273

I saw in Backbone.js source code in several places, like https://github.com/documentcloud/backbone/blob/0.9.2/backbone.js#L273

我想我看到了它在jQuery的源代码中也是如此。并且在多个Js写作风格指南中蓬勃发展。

I think I saw it too in jQuery's source code too. And in the multiple Js writing style guides that flourished.

---编辑2代码示例：

--- edit 2 code example :

var func = function(param, options) {
   // How I do it
   var options = options || {};
   // How I should do it in the "same" way
   options = options || {};
   // The "other" way
   options || (options = {});

}

推荐答案

他们应该做同样的事情，但有一个更好的方法。

They should do the same thing, but there is a better way.

理论上第二个，仅在值为假的情况下进行分配，可以消除分配并加快速度。实际上在jsperf中我们看到它是（12％）。

Theoretically the second, assigning only if the value is falsy, could eliminate an assignment and be faster. Indeed in a jsperf we see it is (12%).

事实上，显式if语句与条件然后分配一样快：

In fact the explicit if statement is just as fast as the condition-then-assign:

if(!options)
    options = {};

在您的浏览器/计算机上尝试测试。

我认为明确的if是最明确的，并且没有惩罚。

I think the explicit if is the most clear, and has no penalty.

编辑：

如果您希望将对象传入函数，那么我认为更好的测试是：

If you are expecting an object to be passed in to a function, then I think the better test is:

if(typeof options !== 'object') 
    options = {};

这将确保您之后有一个对象，即使它是空的。任何其他测试（对于未定义或虚假）将允许真正的非对象通过非零数字或非空字符串。然而，正如jsperf所示，这慢了约15％。由于你只是在进入一个处理对象的函数时这样做，我认为这是一个值得的权衡，并且总是分配的速度慢得多。

This will ensure that you have an object afterwards, even if it is empty. Any other test (for undefined, or falsiness) will permit a truthy non-object through like a non-zero number or a non-empty string. As the jsperf shows, however, this is ~15% slower. Since you only do this on entry to a function which will be processing objects, I would argue that is a worthwhile tradeoff, and is barely slower that the always-assign.

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