Understand promises

understand_promises.js

var Q = require('kew');


function failureSync(){
  throw new Error('sync failure');
};

function failureAsync(){
  return Q.reject(new Error('async failure'));
};

function successSync(){
  return "OK";
};

function successAsync(){
  return Q.resolve("OK");
};

var test1 = Q.resolve().then(failureSync).then(function(){
  console.log('should never be triggered');
}).fail(function(){
  console.log('test 1 - should be triggered');
});

var test2 = Q.resolve().then(failureAsync).then(function(){
  console.log('should never be triggered');
}).fail(function(){
  console.log('test 2 - should be triggered');
}).then(function(){
  console.log('test 2 - should also be triggered');
});

var test3 = Q.resolve().then(failureAsync).then(function(){
  console.log('should never be triggered');
}).fail(function(){
  console.log('test 3 - should be triggered');
  return failureAsync();
}).then(function(){
  console.log('test 3 - should not be triggered');
}).fail(function(){
  console.log('test 3 - should also be triggered');
});

function oneFailureAmongSeveralSuccesses(){
  return Q.all([
    successAsync(), failureAsync(), successAsync()
  ])
};

var test4 = oneFailureAmongSeveralSuccesses().then(function(){
  console.log('should never be triggered');
}).fail(function(err){
  console.log('test oneFailureAmongSeveralSuccesses - should be triggered', err);
});


function oneRescuedFailureAmongSeveralSuccesses(){
  return Q.all([
    successAsync(), failureAsync().fail(function(){
      return 'rescued this one';
    }), successAsync()
  ])
};

var test5 = oneRescuedFailureAmongSeveralSuccesses().fail(function(){
  console.log('should never be triggered');
}).then(function(results){
  console.log('test oneRescuedFailureAmongSeveralSuccesses - should be triggered', results);
});


handle = setInterval(function(){}, 1000);

Q.all([test1, test2, test3, test4, test5]).then(function(){
  clearInterval(handle);
});