ES6 数组解构怪异 [英] ES6 Array destructuring weirdness

问题描述

谁能解释一下，为什么 ES6 数组解构会发生以下情况?

让 a, b, c[a, b] = ['A', 'B'][b, c] = ['BB', 'C']console.log(`a=${a} b=${b} c=${c}`)//预期:a=A b=BB c=C//实际:a=BB b=C c=undefined

http://codepen.io/ronkot/pen/WxRqXg?editors=0011

解决方案

正如其他人所说，您缺少分号.但是……

<块引用>

谁能解释一下?

在您的行之间没有分号自动插入来分隔两个"语句，因为它作为单个语句是有效的.它被解析(和评估)为

let a = undefined, b = undefined, c = undefined;[a, b] = (['A', 'B'][(b, c)] = ['BB', 'C']);console.log(`a=${a} b=${b} c=${c}`);

其中

• [a, b] = …; 是预期的解构赋值
• (... = ['BB', 'C']) 是一个赋值表达式，将数组分配到左侧，并对数组求值
• ['A', 'B'][…] 是一个 属性引用 数组文字
• (b, c) 正在使用 逗号运算符，计算结果为c(即undefined)

如果您想省略分号并让它们自动插入可能需要的地方，您将需要在以(开头的每一行的开始放一个code>、[、/、+、- 或 `.>

Can anyone explain, why the following happens with ES6 array destructuring?

let a, b, c
[a, b] = ['A', 'B']
[b, c] = ['BB', 'C']
console.log(`a=${a} b=${b} c=${c}`)

// expected: a=A b=BB c=C
// actual:   a=BB b=C c=undefined

http://codepen.io/ronkot/pen/WxRqXg?editors=0011

解决方案

As others have said, you're missing semicolons. But…

Can anyone explain?

There are no semicolons automatically inserted between your lines to separate the "two" statements, because it is valid as a single statement. It is parsed (and evaluated) as

let a = undefined, b = undefined, c = undefined;
[a, b] = (['A', 'B']
[(b, c)] = ['BB', 'C']);
console.log(`a=${a} b=${b} c=${c}`);

wherein

• [a, b] = …; is a destructuring assignment as expected
• (… = ['BB', 'C']) is an assignment expression assigning the array to the left hand side, and evaluating to the array
• ['A', 'B'][…] is a property reference on an array literal
• (b, c) is using the comma operator, evaluating to c (which is undefined)

If you want to omit semicolons and let them be automatically inserted where ever possible needed, you will need to put one at the start of every line that begins with (, [, /, +, - or `.

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