js手写-实现Promise的实例方法

catch

等效为Promise.prototype.then(undefined,onRejected)

 then(onFulfilled, onRejected) {return new MyPromise((resolve, reject) => {//定义默认的函数const defaultOnFulfilled = (value) => value;const defaultOnRejected = (reason) => {throw reason;}onFulfilled = onFulfilled || defaultOnFulfilled;onRejected = onRejected || defaultOnRejected;
//省略之后的代码});}catch(onRejected) {return this.then(undefined, onRejected);}

finally

   finally(onFinally) {this.then(onFinally, onFinally);}promise.then((val) => {console.log("then中的成功回调:", val);}).catch((err) => {console.log("catch中的失败回调结果", err);}).finally((e)=>{console.log("finally获得的结果",e);});