因为catch和then的第二个参数，是处理rejected状态的，但是它默认返回的应该是resolved啊。老师这里reject(newReason);不是又返回rejected的状态吗？
还有如果老师我这样理解是对的话pending里面该怎么改呢？

    then(fn1, fn2) {
        // 判断fn1, fn2是不是函数
        fn1 = typeof fn1 === 'function' ? fn1 : (v) => v;
        fn2 = typeof fn2 === 'function' ? fn2 : (e) => e;

        if (this.state === 'pending') {
            // 当pending状态下，fn1和fn2会存储到callbacks中
            return new MyPromise((resolve, reject) => {
                this.resolveCallbacks.push(() => {
                    try {
                        const newValue = fn1(this.value);
                        resolve(newValue);
                    } catch (error) {
                        reject(error);
                    }
                })
                this.rejectCallbacks.push(() => {
                    try {
                        const newReason = fn2(this.reason);
                        reject(newReason);
                    } catch (error) {
                        reject(error);
                    }
                })
            })
        }

        if (this.state === 'fulfilled') {
            // 要返回新的promise，传入当前的value，计算出新的value，resolve
            return new MyPromise((resolve, reject) => {
                try {
                    const newValue = fn1(this.value);
                    resolve(newValue);
                } catch (error) {
                    reject(error);
                }
            })
        }

        if (this.state === 'rejected') {
            // 要返回新的promise，传入当前的reason，生成新的reason，reject
            return new MyPromise((resolve, reject) => {
                try {
                    const newValue = fn2(this.reason);
                    resolve(newValue);  **//这里改为resolve**
                } catch (error) {
                    reject(error);
                }
            })
        }
    }
    // 就是then的语法糖 
    catch(fn) {
        return this.then(null, fn);
    }