实现一个 async 函数

实现一个 async 函数

function async (genertor) {
    let iterator = genertor()
    function handle(lastResult) {
        const {done, value} = lastResult
        if(done) return
        if(value instanceof Promise) {
            value.then(res =>{
                handle(iterator.next(res))
            }).catch(e => {
                 iterator.throw(e)
            })
        } else {
            throw new Error('iterator is not a Promise')
        }
    }

    handle(iterator.next())
}

async(function* () {
    const res1 = yield Promise.resolve(1)
    console.log(1,res1)
    const res2 = yield Promise.resolve(res1 + 1)
    console.log(2,res2)
    const res3 = yield Promise.resolve(res2 + 1)
    console.log(3,res3)
})

// ----输出
// 1 1
// 2 2
// 3 3