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Showing content from https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Errors/Invalid_for-of_initializer below:

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

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)

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。

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

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。

let iterable = [10, 20, 30];

for (let value of iterable) {
  value += 50;
  console.log(value);
}
// 60
// 70
// 80

• for...of
• for...in – 在严格模式下也同样禁止使用初始化器 (SyntaxError: for-in loop head declarations may not have initializers)
• for – 在迭代时允许定义初始化器

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