使用JavaScript进行多次左手分配 [英] Multiple left-hand assignment with JavaScript

问题描述

var var1 = 1,
    var2 = 1,
    var3 = 1;

这相当于：

var var1 = var2 = var3 = 1;

我很确定这是变量定义的顺序：var3，var2，var1，将等同于：

I'm fairly certain this is the order the variables are defined: var3, var2, var1, which would be equivalent to this:

var var3 = 1, var2 = var3, var1 = var2;

有没有办法在JavaScript中确认这个？可能使用某个探查器？

Is there any way to confirm this in JavaScript? Using some profiler possibly?

推荐答案

实际上，

var var1 = 1, var2 = 1, var3 = 1;

不相当于：

var var1 = var2 = var3 = 1;

区别在于范围界定：

function good() {
  var var1 = 1, var2 = 1, var3 = 1;
}

function bad() {
  var var1 = var2 = var3 = 1;
}

good();
console.log(window.var2); // undefined

bad();
console.log(window.var2); // 1. Aggh!

实际上这表明作业是正确的关联。 坏示例相当于：

Actually this shows that assignment are right associative. The bad example is equivalent to:

var var1 = (window.var2 = (window.var3 = 1));

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