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let promise = Promise.resolve();

promise.then(() => alert(" "));

alert(" "); //  alert  

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Promise.resolve()
  .then(() => alert(" !"))
  .then(() => alert(" "));

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let promise = Promise.reject(new Error("  !"));
promise.catch(err => alert('!'));

//  ,  
window.addEventListener('unhandledrejection', event => {
  alert(event.reason);
});

.catch, , , :

let promise = Promise.reject(new Error("  !"));

//   !
window.addEventListener('unhandledrejection', event => alert(event.reason));

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let promise = Promise.reject(new Error("  !"));

setTimeout(() => promise.catch(err => alert('')), 1000);

//   !
window.addEventListener('unhandledrejection', event => alert(event.reason));

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