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const start = Date.now();
return Promise.resolve().
  then(() => new Promise(resolve => setTimeout(resolve, 50))).
  then(() => new Promise(resolve => setTimeout(resolve, 50))).
  then(v => {
    console.log(Date.now() - start); 
  });

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return Promise.resolve(1).
  
  
  
  then(v => new Promise(resolve => setTimeout(() => resolve(v + 1), 10))).
  then(v => new Promise(resolve => setTimeout(() => resolve(v + 1), 10))).
  then(v => new Promise(resolve => setTimeout(() => resolve(v + 1), 10))).
  
  
  then(v => v + 1).
  then(v => {
    console.log(v); 
  });

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Promise.resolve(1).
  then(v => v + 1).
  
  then(() => Promise.reject(new Error('Oops'))).
  then(v => v + 1).
  catch(err => {
    err.message; 
  });

Promise.resolve(1).
  then(v => v + 1).
  
  then(() => { throw new Error('Oops'); }).
  then(v => v + 1).
  catch(err => {
    err.message; 
  });