常见的数组迭代方法有很多种，比如 some, filter, map等等，底层也都可以用for来实现，我们来康一康。

some

    const some = (arr, fn) => {
      for (let i = 0; i < arr.length; i++) {
        if (fn(arr[i], i, arr)) {
          return true
        }
      }
      return false
    }

every

    const every = (arr, fn) => {
      let count = 0
      const len = arr.length
      for (let i = 0; i < len; i++) {
        if (fn(arr[i], i, arr)) {
          count++
        }
      }
      return count === len
    }

filter

    const filter = (arr, fn) => {
      const res = []
      for (let i = 0; i < arr.length; i++) {
        if (fn(arr[i], i, arr)) {
          res.push(arr[i])
        }
      }
      return res
    }

find

    const find = (arr, fn) => {
      for (let i = 0; i < arr.length; i++) {
        if (fn(arr[i], i, arr)) {
          return arr[i]
        }
      }
    }

map

    const map = (arr, fn) => {
      const res = []
      for (let i = 0; i < arr.length; i++) {
        res.push(fn(arr[i]))
      }
      return res
    }

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