everyone knows that the chained call to jQuery is a wonderful use for return this, but what about Promise? For example,

function start() {  
    return new Promise((resolve, reject) => {  
      resolve("start");  
    });  
  }  
    
  start()  
    .then(data => {  
      // promise start  
      console.log("result of start: ", data);  
      return Promise.resolve(1); // p1  
    })  
    .then(data => {  
      // promise p1  
      console.log("result of p1: ", data);  
      return Promise.reject(2); // p2  
    })  
    .then(data => {  
      // promise p2  
      console.log("result of p2: ", data);  
      return Promise.resolve(3); // p3  
    })  
    .catch(ex => {  
      // promise p3  
      console.log("ex: ", ex);  
      return Promise.resolve(4); // p4  
    })  
    .then(data => {  
      // promise p4  
      console.log("result of p4: ", data);  
    });  

result of start: start
result of p1: 1
ex: 2
result of p4: 4

the third step, reject is also ignored by the next step of then. What is the principle of this chained call? How did it happen?