This chapter covers
- What promises are and why they're important
- The
Deferredobject - How to manage multiple asynchronous operations
- Resolving and rejecting a promise
13.1 Introduction to promises
13.2 The Deferred and Promise objects
13.3 The Deferred methods
$.Deferred([beforeStart])
Parameters
beforeStart (Function)
Returns
The Deferred Object.
13.3.1 Resolving or rejecting a Deferred
deferred.resolve([argument, ..., argument])
Parameters
argument (Any)
Returns
The Deferred object.
deferred.resolveWith(context[, argument, ..., argument])
Parameters
context (Object)
argument (Any)
Returns
The Deferred object.
deferred.reject([argument, ..., argument])
Parameters
argument (Any)
Returns
The Deferred object.
deferred.rejectWith(context[, argument, ..., argument])
Parameters
context (Object)
argument (Any)
Returns
The Deferred object.
13.3.2 Execute functions upon resolution or rejection
deferred.done(callbacks[, callbacks, ..., callbacks])
Parameters
callbacks (Function|Array)
Returns
The Deferred object.
deferred.fail(callbacks[, callbacks, ..., callbacks])
Parameters
callbacks (Function|Array)
Returns
The Deferred object.
13.3.3 The when() method
$.when(object[, object, ..., object])
Parameters
object (Deferred|Promise|Object)
Returns
A Promise object
function success() {}
function fail() {}
$.when($.ajax('integer.php'), $.ajax('integer.php')).done(success).fail(fail);
13.3.4 Notifying about the progress of a Deferred
deferred.notify([argument, ..., argument])
Parameters
argument (Any)
Returns
The Deferred object.
deferred.notifyWith(context[, argument, ..., argument])
Parameters
context (Object)
argument (Any)
Returns
The Deferred Object.
13.3.5 Follow the progress
*** deferred.progress(callbacks[, callbacks, ..., callbacks])***
Parameters
callbacks (Function|Array)
Returns
The Deferred object.
var deferred = $.Deferred().progress(function (value) {
$('.progress').text(Math.floor(value) + '%');
});
13.3.6 Using the Promise object
deferred.promise([target])
Parameters
target (Object)
Returns
The Promise object.
function timeout(milliseconds) {
var deferred = $.Deferred();
setTimeout(deferred.resolve, milliseconds);
return deferred.promise();
}
timeout(1000).done(function() {
alert('I waited for 1 second!');
});
13.3.7 Take it short with then()
deferred.then(resolvedCallback[. rejectedCallback[, progressCallback]])
Parameters
resolvedCallback (Function)
rejectedCallback (Function)
progressCallback (Function)
Returns
A Promise object
animate(1000).then(
function() {
alert('The process is completed');
},
null,
function (value) {
$('.progress').text(Math.floor(value) + '%');
}
);
13.3.8 Always execute a handler
deferred.always(callbacks[, callbacks, ..., callbacks])
Parameters
callbacks (Function|Array)
Returns
The Deferred object.
var deferred = $.Deferred();
deferred
.then(
function(value) {
console.log('success: ' + value);
},
function(value) {
console.log('fail: ' + value);
}
)
.always(function() {
console.log('I am always logged');
});
deferred.reject('An error');
13.3.9 Determine the state of a Deferred
deferred.state()
Returns
A string representing the state of the Deferred.
assert.equal(deferred.state(), 'resolved');
13.4 Promisifying all the things
promise([type][, target])
Parameters
type (String)
target (Object)
Returns
A Promise object.
$('#square1').animate({left: 500}, 1500);
$('#square2').animate({left: 500}, 3000);
$('.square')
.promise()
.done(function() {
alert('The animations are completed');
});
13.5 Summary
deferred.resolve()
deferred.reject()
deferred.notify()
deferred.resolveWith()
deferred.rejectWith()
deferred.notifyWith()
deferred.done()
deferred.fail()
deferred.progress()
deferred.always()
deferred.state()