JavaScript OR（||）变量赋值说明 [英] JavaScript OR (||) variable assignment explanation

问题描述

给出这段JavaScript代码......

Given this snippet of JavaScript...

var a;
var b = null;
var c = undefined;
var d = 4;
var e = 'five';

var f = a || b || c || d || e;

alert(f); // 4

有人可以向我解释一下这种技术的用途（我的最佳猜测是在这个问题的标题！）？它是如何/为什么它正常工作？

Can someone please explain to me what this technique is called (my best guess is in the title of this question!)? And how/why it works exactly?

我的理解是变量 f 将被赋予第一个变量的最近值（从左到右）它的值不是null或未定义，但是我没有找到很多关于这种技术的参考资料，并且看到它使用了很多。

My understanding is that variable f will be assigned the nearest value (from left to right) of the first variable that has a value that isn't either null or undefined, but I've not managed to find much reference material about this technique and have seen it used a lot.

此外，这种技术是否特定于JavaScript？我知道在PHP中做类似的事情会导致 f 有一个真正的布尔值，而不是 d 本身的值。

Also, is this technique specific to JavaScript? I know doing something similar in PHP would result in f having a true boolean value, rather than the value of d itself.

推荐答案

参见短路评估的解释。这是实现这些运营商的常用方式;它不是JavaScript独有的。

See short-circuit evaluation for the explanation. It's a common way of implementing these operators; it is not unique to JavaScript.

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