CODEWITHSUNDEEP
javascriptnode.js
user1592380
user1592380

Reputation: 36247

Success and rejection handlers added to Promise do not activate

This is a basic question. I'm working through a js/node workshop on async programming called promise-it-wont-hurt. I have the following exercise:

// Let’s build a simple script to prove to ourselves that promises may only
// resolve one time and all future attempts to resolve them will simply be ignored.

// First, create a promise using the Promise constructor as we have been doing.

// In the promise’s executor, immediately attempt to fulfill the promise with a
// value of 'I FIRED'.

// Then, after the fulfill call, immediately try to reject the promise with an
// Error created with parameter 'I DID NOT FIRE'.

// After the promise creation, create a function onRejected with one parameter
// error that prints the Error’s message with console.log.

// Lastly, pass console.log and the function you just created as the success
// and rejection handlers respectively.

// If successful, your script should only log “I FIRED” and should not log
// “I DID NOT FIRE”.

my test.js contains:

var promise = new Promise(function(resolve, reject) {
  () => {resolve("I FIRED")},  
  ()  => {   reject(new Error("I DID NOT FIRE"))}
});

function onReject (error) {
  console.log(error.message);
}

promise.then(x =>console.log(x),error =>onReject(error))

I'm a little unsure about:

// Lastly, pass console.log and the function you just created as the success
// and rejection handlers respectively.

I've rewritten this as:

promise.then(x =>console.log(x),error =>onReject(error))

However this produces no output at the command line. Experts can you please explain where my error is?

Upvotes: 0

Views: 129

Answers (2)

marsh
marsh

Reputation: 156

You need to return the promise.

const madeOrder = bool => new Promise((res,rej) => {
   if(bool) res('HE MADE AN ORDER!');
   rej('HE DIDNT MAKE AN ORDER :(');
})

madeOrder(true)
  .then(res => console.log(res))
  .catch(err => console.log(err));

Upvotes: 1

NotARealProgrammer
NotARealProgrammer

Reputation: 56

Also new to JS Promises, but I believe this is because the resolve() and reject() are inside of their own functions that are not called.

I tried changing the promise to this:

var promise = new Promise(function(resolve, reject) {
    resolve("I FIRED");
    reject(new Error("I DID NOT FIRE"));
});

It seemed to have the desired efffect when I tested in the Chrome DevTools Console.

Upvotes: 3

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