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);
})
;