1. Generator

1.1 使用方法

function * loop () {
    for (let i = 0; i < 4; i++) {
        yield console.log(i)
    }
}

const l = loop()

l.next() // 1
l.next() // 2
l.next() // 3
l.next() 

1.2 next

function * gen () {
    let val 
    val = yield [1, 2, 3]
    console.log(val)
}

let l = gen()
l.next() // {value: [1, 2, 3], done: false}  value是当前的值 done是函数是否结束
l.next()

yield * 表示后面是一个可迭代的对象，并且还可以是一个Generator函数

function * gen () {
    let val 
    val = yield * [1, 2, 3]
    console.log(val)
}
let l = gen()
l.next() // {value: 1, done: false}
l.next() // {value: 2, done: false}
l.next() // {value: 3, done: false}
l.next() // {value: undefined, done: true}

1.3 控制函数内部运行数据

function * gen () {
    let val 
    val = yield [1, 2, 3]
    console.log(val)
}

let l = gen()
l.next(10) // 找到第一个yield 解析后面数组 结束
l.next(20) // 改变yield返回值 赋值给val

1.4 中止generator

function * gen () {
    let val 
    val = yield [1, 2, 3]
    console.log(val)
}

let l = gen()
l.next(10) // 找到第一个yield 解析后面数组 结束
l.return() // 终止generator

1.5 generator抛出异常 捕获异常

function * gen () {
    while (true) {
        try {
            yield 1
        } catch (e) {
            console.log(e)
        }
    }
}

const l = gen()
console.log(l.next())
console.log(l.next())
console.log(l.throw(new Error('error')))
console.log(l.next())

2.Iterator

2.1 如何让不支持遍历的数据结构“可遍历”

let authors = {
    example: {
        a: [1,2,3],
        b: [3,4,5]
    },
    test: [2,4]
}

authors[Symbol.iterator] = function () {
    let allAuthors = this.example // this就是authors
    let keys = Object.keys(allAuthors)
    let values = []
    return {
        next () {
            if (!values.length) {
                if (keys.length) {
                    values = allAuthors[keys[0]]
                    keys.shift()
                    
                }
                
            }
            return {
                done: !values.length,
                value: values.shift()
            }
        }
    }
}

let r = []
for (let value of authors) {
    r.push(value)
}
console.log(r)

2.2 Generator写法

let author = {
  allAuthor: {
    china: ['a', 'b', 'c'],
    japan: ['n', 'd', 's'],
    other: [1, 2, 3]
  }
}

author[Symbol.iterator] = function * () {
  let authors = this.allAuthor
  let keys = Object.keys(authors)
  let values = []

  while (true) {
    if (!values.length) {
      if (keys.length) {
        values = authors[keys[0]]
        keys.shift()
        yield values.shift()
      } else {
        return false
      }
    } else {
      yield values.shift()
    }
  }
}

let result = []
for (let value of author) {
  result.push(value)
}
console.log(result)