JS - 用 for 循环实现常见的数组迭代方法

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

1    const some = (arr, fn) => {
2      for (let i = 0; i < arr.length; i++) {
3        if (fn(arr[i], i, arr)) {
4          return true
5        }
6      }
7      return false
8    }

every

1    const every = (arr, fn) => {
2      let count = 0
3      const len = arr.length
4      for (let i = 0; i < len; i++) {
5        if (fn(arr[i], i, arr)) {
6          count++
7        }
8      }
9      return count === len
10    }

filter

1    const filter = (arr, fn) => {
2      const res = []
3      for (let i = 0; i < arr.length; i++) {
4        if (fn(arr[i], i, arr)) {
5          res.push(arr[i])
6        }
7      }
8      return res
9    }

find

1    const find = (arr, fn) => {
2      for (let i = 0; i < arr.length; i++) {
3        if (fn(arr[i], i, arr)) {
4          return arr[i]
5        }
6      }
7    }

map

1    const map = (arr, fn) => {
2      const res = []
3      for (let i = 0; i < arr.length; i++) {
4        res.push(fn(arr[i]))
5      }
6      return res
7    }

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