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yarn

Yarn is a simple asynchronous routing pattern that makes it easy to write asynchrounous code in linear fashion.

Setup

To set up yarn on your Node.js server use npm.

npm install yarn

If you want to use yarn on the client-side (browser), just include yarn.js into your page.

<script type='text/javascript' src='yarn.js'></script>

Using yarn

Using yarn is simple. First, you have to do is require the yarn function (if you're using it client-side, this isn't necessary).

var yarn = require('yarn');

Then, you can call yarn and pass it an initial function, and then chain sets of functions after.

yarn
(function(){
    this(0)();
})
(function(){

},
function(){

});

In the initial function (the first one), this is a function which returns one of next functions in the next set of functions. For example, this(0) would return the first function, and this(1) would return the second function. Every function in the series has a this function which returns one of the functions in the next set.

yarn
(function(){
    this(Math.round(Math.random()))();
})
(function(){
    this(0)();
},
function(){
    this(1)();
})
(function(){
    console.log('made it to the first of final set');
},
function(){
    console.log('made it to the second of final set');
});

Here is an example of how you could use yarn with asynchronous callbacks.

yarn
(function(){
    doSomethingAsynchronous(this());
})
(function(err){
    // this(0) returns error function, and this(1) returns success function
    if (err)
        this(0)();
    else
        this(1)();
})
(function error(){
    alert('Aww...');
},
function success()
    alert('Yay!!!');
});

function doSomethingAsynchronous(callback) {
    setTimeout(function(){
        if (Math.round(Math.random()) == 0)
            callback(true);
        else
            callback(false);
    }, 1000);
}

Another thing to note is that this() (called with no index passed) is synonymous to this(0).

to be conitnued...possibly

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