关于 ES6 数组解构和交换的有趣行为

Question

我只是注意到以下代码，如果没有立即引用oneafter let [one, two] = [1, 2]，尝试[one, two] = [two, one]会崩溃：

let [one, two, three] = [1, 2, 3]
[one, two] = [two, one] // CRASH! one is not defined
console.log(one, two)

然而，简单地one在声明和交换之间添加一个 not-used突然允许代码，但不正确：

let [one, two, three] = [1, 2, 3]
one // inserted here
[one, two] = [two, one] // no longer crashes! but not actually swapping
console.log(one, two) // should be '2 1', but shows '1 2' instead

而下面的代码给出了预期的交换效果

var a = 1;
var b = 3;

[a, b] = [b, a];
console.log(a); // 3
console.log(b); // 1

有人可以解释为什么存在这种行为吗？谢谢！

Answer 1

在第一行添加一个分号，因为解释器假定第 1 行和第 2 行声明一起发生，并且one(and two) 尚未定义：

let [one, two, three] = [1, 2, 3];
[one, two] = [two, one]
console.log(one, two)