chainLoading

Allows you to chain together deferreds or functions and control the order at which they call your callbacks. The benefit being that all methods are called immediately and the callbacks are called in the order you want. This can make loading a page that requires multiple API calls much faster since the API calls will happen in parallel.

This library officially supports jQuery's deferreds and q's deferreds. Any class with then should work though.

Let's get straight into an example for rendering a user's profile page:

var chain = new ChainLoading();
//first thing we need is to fetch the template
chain.push(this.fetchTemplate('myPage.ejs')).done(_.bind(this.renderTemplate, this));
//we want to fetch the user's profile from the backend immediately, but delay calling
//renderUserProfile until the template was rendered
chain.push(this.loadUserProfile()).done(_.bind(this.renderUserProfile, this));
//fetch the comments immediately and render them on the same "level" as the user profile
//also we don't need to fail the WHOLE page if it fails to fetch comments, so ignoreFail
chain.addIgnoreFail(this.loadComments()).done(_.bind(this.renderComments, this));
chain.fail(_.bind(this.renderPageFailed, this));

The order is controlled by squential "levels". A "level" will not get resolved until the previous "level" is resolved. If a deferred is rejected, none of the callbacks in levels after it in the chain will be called unless you used one of the ignore methods.

If you're upgrading from 0.2.x, please see the "upgrade notes" section below

Simple Usage

var chain = new ChainLoading();
//myCallback will get called first
chain.push($.get('http://example.com/1')).done(myCallback);
//myCallback2 will get called second
chain.push($.get('http://example.com/2')).done(myCallback2);

push(deferred)

Adds the deferred to a new "level". This method returns a deferred that you must call done, then, always, or fail on to know when the deferred is finished. Arguments are passed through from the deferred that completed.

Note: then does not support chanining. It returns the promise it was called on. Use chainLoading for chaining ;)

add(deferred)

Adds the deferred to the current "level". This method returns a deferred. Order is not guaranteed within a "level". If you require order, then always use push. This is useful when you have a group of deferreds that are independent of each other but all depend on an earlier "level".

pushIgnoreFail(deferred)

Same as push() except that any failures will not cause the chain to stop. Only fail callbacks attached to the deferred that is returned will get called (global fail callbacks and future-level fail callbacks will NOT get called).

addIgnoreFail(deferred)

Same as pushIgnoreFail() except it adds the deferred to the current "level".

after(func)

Adds a function to be called once the previous "levels" complete. Useful at the end of all your deferreds for knowing when everything completed.

fail(func)

func is called once whenever previous "levels" failed. Useful at the end of all your deferreds for knowing if the chain failed. A fail callback added at the very beginning of a chain (before any push's or add's) is called once when ANY level fails. func is passed the arguments that were passed to the deferred that failed.

promise()

Returns a promise object with done, fail, always, then function that map to each of the chain's methods. Useful to return at the end of a function utilizing a chain so the caller can do func().done(itsDone) to know when the function is done.

Note: then does not support chanining. It returns the promise it was called on. Use chainLoading for chaining ;)

state()

Returns the current state of a the chain. It can be rejected, resolved, or pending. If the chain was stopped via stop() the state will be rejected. Ignored fails will NOT cause the state to be rejected.

Upgrade notes

If you're coming from 0.2.x release then you'll notice a few things changed:

• Usage of chain.bind is now deprecated
• fail will only be called when previous "levels" failed instead of every fail callback always being called.

Advanced usage

push(deferred, ..., deferredn)

push/add/etc all support multiple deferreds. The done callback will get called once ALL the deferreds have resolved and the arguments will be all of the deferreds results combined.

chain.push(d1, d2, d3).done(function(one, two, three) {});
d1.resolve(1);
d2.resolve(2);
d3.resolve(3);

storeArgs(arg1, ..., argn)

If you want to store the resulting arguments on the chain for later use by applyArgs then send this function to a deferred's done.

storeArgs does NOT support currying, so dfd.done(chain.storeArgs(1)) will ONLY store 1 regardless of what is resolved. Instead you can do dfd.done(chain.storeArgs(1)).done(chain.storeArgs)

Keep in mind that if you're using pushIgnoreFail args will not be stored on fail unless you do something like fail(chain.storeArgs(null)). Failure arguments can be unexpected so a decision was made to not add them by default.

chain.push(myDfd).done(chain.storeArgs));
chain.after(chain).storeArgs("finished myDfd"));
chain.push(mySecondDfd).done(chain.applyArgs(myCallback, this));
//{myCallback} will get args from myDfd, then "finished myDfd", then args from mySecondDfd

applyArgs(func, context, [arg1, ..., argn])

Applies arguments stored using storeArgs to func. Can be used instead of a bind function. This does support currying so feel free to use this on your last deferred.

fork()

Returns a NEW chain that's dependent on the current level of this chain but will then run independently of this chain. You can bring the 2 back together using push/add later if you choose.

stop()

Immediately stops calling ANY callbacks, including fail callbacks. The chain is unusable after this is called. You should use this for places where you don't want two different instances of a chain running at the same time.

Caveats

• Does not emit progress events for deferreds that utilize notify.

By James Hartig