understanding promises javascript code example

Example 1: javascript promise

var promise = new Promise(function(resolve, reject) {
  // do some long running async thing…
  
  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }
  else {
    reject(Error("It broke"));
  }
});

//usage
promise.then(
  function(result) { /* handle a successful result */ },
  function(error) { /* handle an error */ }
);

Example 2: javascript promises

firstRequest()
  .then(function(response) {
    return secondRequest(response);
}).then(function(nextResponse) {  
    return thirdRequest(nextResponse);
}).then(function(finalResponse) {  
    console.log('Final response: ' + finalResponse);
}).catch(failureCallback);