HTML and CSS Reference
In-Depth Information
14.4.1.2 Rejecting the Promise
Next up, we'll start changing the original tests to work with promises. The first test
we wrote expects
addMessage
to call the callback, passing an error if no username
is passed to it. The updated test can be seen in Listing 14.48.
Listing 14.48
Using the returned promise
"should require username": function (test) {
var promise = this.room.addMessage(null, "message");
promise.then(function () {}, function (err) {
test.isNotNull(err);
test.inherits(err, TypeError);
test.done();
});
}
The promise has a
then
method, which allows consumers to add callbacks to
be called when it is fulfilled. It accepts one or two functions; the first function is the
success callback and the second is the error callback. Another way of doing this is
to use the
addCallback
and
addErrback
methods, but I like the way “then”
reads:
addMessage(user, msg).then(callback)
.
To pass this test, we need to duplicate some efforts in
addMessage
, as we're
not yet ready to drop the old implementation. Listing 14.49 shows the updated
method.
Listing 14.49
Updating
addMessage
addMessage: function (user, message, callback) {
var promise = new Promise();
process.nextTick(function () {
/* ... */
if (err) {
promise.reject(err, true);
}
}.bind(this));
return promise;
}
Here we call the promise's
reject
method, passing it an error. Normally,
the promise will throw an exception if
reject
is called and no error handler is
