迭代器

不要使用 iterators，建议使用 JS 更高优先级的函数代替 for-in 或 for-of 循环，除非迫不得已，eslint: no-iterator no-restricted-syntax

const numbers = [1, 2, 3, 4, 5]

// bad
let sum = 0
for (let num of numbers) {
  sum += num
}

// good
let sum = 0
numbers.forEach(num => sum += num)

// better
const sum = numbers.reduce((total, num) => total + num, 0)