Andy Ray Andy Ray - 3 months ago 33
jQuery Question

attempting to break jQuery promise chain with .then, .fail and .reject

Update: this issue was a result of jQuery 1.7 vs 1.8. Do not ever use promises in 1.7 beacuse they aren't chainable with returning a promise inside a

.then
. 1.8 looks like they didn't mess it up.

http://jsfiddle.net/delvarworld/28TDM/

// make a promise
var deferred = $.Deferred();
promise = deferred.promise();

// return a promise, that after 1 second, is rejected
promise.then(function(){
var t = $.Deferred();
setTimeout(function() {
console.log('rejecting...');
t.reject();
}, 1000);

return t.promise();
});

// if that promise is successful, do this
promise.then(function() {
console.log('i should never be called');
})

// if it errors, do this
promise.fail(function() {
console.log('i should be called');
});

deferred.resolve();


Expected: 'i should be called'

Actual: 'i should never be called'

Problem: I want to chain callbacks and have any one of them be able to break the chain and trigger the
fail
function, and skip the other chained callbacks. I don't understand why all of the thens are triggered and the fail is not triggered.

I'm coming from NodeJS's Q library, so I tried it with
.then
first. However, changing it to
.pipe
has no effect.

Answer

You aren't re-defining the value of promise, try this:

http://jsfiddle.net/28TDM/1/

var deferred = $.Deferred();
promise = deferred.promise();

promise = promise.then(function(){
    var t = $.Deferred();
    setTimeout(function() {
        console.log('rejecting...');
        t.reject();
    }, 1000);

    return t.promise();
});

promise.then(function() {
    console.log('i should never be called');
})

promise.fail(function() {
    console.log('i should be called');
});

deferred.resolve();

Apparently it does work the way you thought it did, it just isn't documented https://api.jquery.com/deferred.then. Very cool. This is new functionality added in jQuery 1.8.0, more than likely they just aren't done updating the documentation.