使用generator處理無限數據流

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Example

假設現在有一個數據非常多的數組,但是我們只需要它的前幾個數據,并且進行一定的操作,這時候可以使用 generator 來進行 take 的操作.

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const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]
const from = (arr) => arr[Symbol.iterator]()

const filter = (f) =>
  function* (iter) {
    let v = iter.next()
    while (!v.done) {
      if (f(v.value)) yield v.value
      v = iter.next()
    }
  }

const multipy = (n) =>
  function* (iter) {
    let v = iter.next()
    while (!v.done) {
      yield v.value * n
      v = iter.next()
    }
  }

const take = (n) =>
  function* (iter) {
    let i = 0
    let v = iter.next()
    while (!v.done && i < n) {
      yield v.value
      i++
      v = iter.next()
    }
  }

const pipe = (...arr) => arr.reduce((acc, func) => func(acc))

console.log([
  ...pipe(
    from(arr),
    filter((v) => v % 2 === 0),
    multipy(3),
    take(30),
    filter((v) => v > 15)
  ),
]) // [18, 24, 30, 36]