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SyntaxError: a declaration in the head of a for-of loop can't have an initializer

错误信息

SyntaxError: a declaration in the head of a for-of loop can't have an initializer (Firefox) SyntaxError: for-of loop variable declaration may not have an initializer. (Chrome)

本文内容

错误类型

SyntaxError

哪里出错了？

for...of 循环的头部包含有初始化表达式。也就是对一个变量进行声明并赋值 |for (var i = 0 of iterable)|。这在 for-of 循环中是被禁止的。你想要的可能是允许包含初始化器的 for 循环形式。

示例

非法的 for-of 循环形式

js
let iterable = [10, 20, 30]; for (let value = 50 of iterable) { console.log(value); } // SyntaxError: a declaration in the head of a for-of loop can't // have an initializer

合法的 for-of 循环形式

需要将初始化器 (value = 50) 从for-of 循环的头部移除。或许你的本意是给每个值添加 50 的偏移量，在这种情况下，可以在循环体中进行添加。

js
let iterable = [10, 20, 30]; for (let value of iterable) { value += 50; console.log(value); } // 60 // 70 // 80

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