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

问题描述

给定这段 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叫什么吗(我最好的猜测是在这个问题的标题中！)?以及它如何/为什么完全起作用?

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 将被分配到第一个变量的最近值(从左到右)，该变量的值既不是 null 也不是未定义，但我没有设法找到了很多关于这种技术的参考资料，并且已经看到它被大量使用.

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，这项技术是否特定于 JavaScript?我知道在 PHP 中做类似的事情会导致 f 具有真正的布尔值，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.这是实现这些运算符的常用方法；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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