先来个例题 看一下结果
function* addGen(x) {
let y = (yield x + 5) * 2
let z = yield y / 4
return x + y + z
}
let g = addGen(1)
console.log(g.next()) // 1> {value: 6, done: false}
console.log(g.next()) // 2> {value: NaN, done: false}
console.log(g.next()) // 3> {value: NaN, done: true}
/*
1> g.next() 返回的 value 是 x + 5 => 6
2> g.next() 返回的 value 是 y / 3，由于本次 g.next() 并未传值，所以 y = undefined * 2 => NaN，所以本次的 value 是 NaN / 3 => NaN
3> g.next() 返回的 value 是 x + y + z => 1 + NaN + NaN => NaN
*/
如何让以上代码执行的更符合一般的逻辑 y = (1 + 5) * 2 ; z = y / 4，最后返回 16
function* addGen(x) {
let y = (yield x + 5) * 2
let z = yield y / 4
return x + y + z
}
let g = addGen(1)
let v1 = g.next().value
let v2 = g.next(v1).value
let v3 = g.next(v2).value
console.log(v3)
再来个实例，以 “敲七” 这个游戏为例，从零开始获取每一个符合 “敲七” 的数字
function* count7Gen(count = 1) {
while (true) {
if (count % 7 === 0 || count % 10 === 7) {
yield count
}
count++
}
}
const c7g = count7Gen()
console.log(c7g.next()) // {value: 7, done: false}
console.log(c7g.next()) // {value: 14, done: false}
console.log(c7g.next()) // {value: 17, done: false}
console.log(c7g.next()) // {value: 21, done: false}
console.log(c7g.next()) // {value: 27, done: false}
count7Gen这个函数本身是一个死循环，但是Generator这种模式使其能在特定的节点停止或继续
模拟一个简单的 Generator
const makeGenerator = (list) => {
let index = 0
return {
next: () => {
const value = list[index++]
const done = index >= list.length
return { value, done }
}
}
}
const g = makeGenerator(['a', 'b', 'c'])
console.log(g.next())
console.log(g.next())
console.log(g.next())
console.log(g.next())