why .then() is getting called twice in promises {javascript}

Problem: last 2 .then are getting called even while i am returning Promise.reject().

1st .then() is printing undefined and 2nd .then() is also printing the output

can someone please explain why?

let p4 = new Promise((resolve,reject)=>{
    resolve("p4 Resolved");
    });

p4.then((val)=>{
    console.log(val);
    return Promise.reject("20 Rejected"); }
    )
    .catch((error)=>{console.log(error)})
    .then((val)=>{console.log(val);return 290})
    .then((val)=>{console.log("Last then : "+val);})
    ;

>Solution :

catch also returns a promise and since you didn’t return anything, it will be a promise that fulfills to undefined, therefore the first then prints undefined. Finally, the last then gets the value 290 from the previously returned promise by the first then and prints it.