逗号运算符如何在js中工作? [英] How does the comma operator work in js?

问题描述

我试图了解逗号运算符(，)在JavaScript中的工作方式， 当它不放在括号之间时，它似乎具有不同的行为.

I'm trying to understand how the comma operator (,) works in JavaScript, it seems to have a different behaviour when it's not put between parenthesis.

有人可以解释我为什么吗?

Can someone explain me why ?

示例供参考:

var a = 1; 
var b = 2; 
var c = (a,b);
console.log(c);
//output : as expected 
var c = a,b;
console.log(c);
//output : 1 

标题可能有点混乱. 我的问题是关于昏迷运算符和var归因之间的误解，正如somone解释的那样更进一步

The title might be a bit confusing. My question is about a misconception between the coma operator and var attribution as somone explained further down

因此，此主题不是是该主题的重复

Therefore this subject is not a duplicate of that one What does a comma do in JavaScript expressions?

推荐答案

var c = (a,b);

上面使用逗号运算符.它的值为右手边的值(即b).

The above uses the comma operator. It evaluates as the value of its right-hand side (i.e. b).

var c = a,b;

这不使用逗号运算符.

此处的逗号字符构成var表达式的一部分，该表达式采用逗号分隔的变量列表在当前作用域中创建，每个变量都可以具有可选的赋值.

The comma character here forms part of the var expression which takes a comma-separated list of variables to create in the current scope, each of which can have an optional assignment.

等效于:

var c = a;
var b;

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