`.catch()` doesn't stop the rest of a promise chain from executing

catch-doesnt-stop-promise-chain.js

// returns a promise that always rejects
function myPromise() {
  return new Promise((resolve, reject) => {
    reject('error in myPromise');
  });
}

// promise.catch(a).then(b).catch(c)
myPromise().catch(function a(err) {
    console.log('a:', err);
    return 'return in a';
  }).then(function b(result) {
    console.log('b:', result);
    throw 'error in b';
  }).catch(function c(err) {
    console.log('c:', err);
  });
/* Output:
a: error in myPromise
b: return in a
c: error in b
*/

// promise.then(x1, x2).then(y).catch(z)
myPromise().then(function x1(result) {
    console.log('x1:', result);
    return 'return in x1';
  }, function x2(err) {
    console.log('x2:', err);
    return 'return in x2';
  }).then(function y(result) {
    console.log('y:', result);
    throw 'error in y';
  }).catch(function z(err) {
    console.log('z:', err);
  });
/* Output:
x2: error in myPromise
y: return in x2
z: error in y
*/