20行实现最简链式调用promise（转）

// 为了简化拆解，这里只实现then

        class myPromise {
            constructor(fn) {
                this.cbs = []
                const res = (data) => {
                    this.cbs.forEach(n => {
                        this.data = data
                        n(data)
                    })
                }
                fn(res)
            }
            then(onRes) {
                return new myPromise((resolve) => {
                    this.cbs.push(() => {
                        const res = onRes(this.data)
                        if (res instanceof myPromise) {
                            res.then(resolve)
                        }
                        else {
                            resolve(res)
                        }
                    })
                })
            }
        }