chain.js is a microframework for handling asynchronous JavaScript - 699 bytes gzipped

It comes with built-in methods for running functions sequentially or in parallel, and lets you define your own methods to handle complex logic (e.g load.js).

run()

Run each argument in parallel and then progress to the next method in the chain once all are complete

run(func1, func2).then(func3, func4);

chain()

Run each function sequentially

chain(func1, func2, func3).then(func4); // => equivalent to run(func1).then(func2).then(func3).then(func4);

defer()

Defer execution of the next method in the chain

defer(500).thenRun(func1); //Delay execution for 0.5s

We can combine built-ins to handle more complicated logic

run(func1, func2).then(func3, func4).thenChain(func5, func6).thenRun(func7);

Some things to note:

• then() is an alias for the previous method in the chain
• all methods have their own then alias - e.g. run() === thenRun()
• separate chains run in their own context

Adding your own methods

load.js (this code in particular) is an example of what you can do with chain.js - it allows you to lazy load scripts in the browser and easily handle complex dependency chains

//Load script1 and script2 in parallel - when they're complete, load script3

load('script1.js', 'script2.js').then('script3.js').thenRun(function () {
    console.log('Done.');
});

Or maybe we need to defer loading a script

defer(500).thenLoad('myscript.js');

Another example

var num = 0;
addMethod('add', function (args, argc) {
    while(argc--) num += args[argc];
    this.next(true); //Call the next method in the chain
});

add(1, 2, 3).then(4, 5, 6); //num === 21

But wait. How do we know when a function is complete?

Synchronous functions are complete when they return something other than null

Asynchronous functions are complete when they call next() - next is passed as the first argument to each function in the chain

run(function (next) {
    setTimeout(function () {
        //Do something..
        next();
    }, 100);
});

Passing state along the chain

All functions are called in the same context so variables can be shared using this

run(function () {
    this.foo = 'bar';
    return true;
}).then(function () {
    console.log(this.foo); //'bar'
});

Error handling

Use the onError method for adding an error handler. All methods in the chain are passed an error callback as the second argument and wrapped in a try..catch

onError(function (err) {
    //Handle the error
}).thenRun(function (next, error) {
    error('Something went wrong');
});

With async functions, it's ok to define the error handler at the end of the chain

run(async1, async2).then(async3).onError(my_handler);

Installation

Bundle chain-min.js or run npm install chain

License

(MIT License)

Copyright (c) 2010 Chris O'Hara cohara87@gmail.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.