jschain

Chain style sequentially programming for Javascript asynchronous jobs.

Javascript Chain

This is a small javascript function to rescue you from infinite callbacks.

npm install jschain
var _map = 
{
    foofunction(next)
    {
        console.log('foo');
        setTimeout(next,1000);
    },
    barfunction(a,b,next)
    {
        console.log('bar: '+a+' '+b);
        setTimeout(next,1000);
    }
};
 
new JSChain(_map).foo().bar('hello','world').exec(function(next)
{
    console.log('cumtome function');
    setTimeout(next,1000);
}).end(function()
{
    console.log('done');
});

##When to use it?##

Javascript callbacks may looks like this:

ajaxGet('http://something',function(a)
{
    saveToDatabase(a,function(err)
    {
        if (!err)
        {
            notifyUser(123,function()
            {
                markNotified(123,function()
                {
                    //done 
                });
            });
        }
    })''
});

The traditional callback style is no longer suitable for heavy event driven style programming.

Now, see what JSChain can do:

new JSChain(
{
    foofunction(next)
    {
        console.log('foo');
        setTimeout(next,1000);
    },
    barfunction(a,b,next)
    {
        console.log('bar: '+a+' '+b);
        setTimeout(next,1000);
    }
}).foo().bar('hello','world').exec(function(next)
{
    console.log('cumtome function');
    setTimeout(next,1000);
}).end(function()
{
    console.log('done');
});

With the help of JSChain, the first demo code could be written like this:

var myController = 
{
    ajaxGetfunction(next) {  ... ... next(); ... },
    saveToDatabasefunction(a,next){ ... ... next(); },
    notifyUserfunction() {  ... next(); },
    markNotifiedfunction(next){ ... next(); ... }
};
 
new JSChain(myController).ajaxGet().saveToDatabase().notifyUser().markNotified();

And JSChain is very useful for data scraping projects:

function getURL(url,next)
{
    console.log('getting '+url);
    setTimeout(function()
    {
        console.log('done');
        next();
    },1000);
}
 
 
var chain = new JSChain({getURL: getURL});
for(var i=1;i<100;i++)
{
    chain.getURL('http://example.com/'+i);
}

The JSChain itself is very small. The full documented source code of JSChain is only 1.6KB. I can paste the source code here, so you can read the source code. This could help you understand how it works.

function JSChain(obj)
{
    var self = this;
    this.____items = []; //this remembers the callback functions list 
    this.____finally = null;
    this.____next = function(jump)  //execute next function 
    {
        if (!jump)
        {
            var func = self.____items.shift();
            if (func) func.call();
        }
        else self.____items = [];
        
        if (self.____items.length == 0 && typeof self.____finally == 'function')
        {
            self.____finally.call(obj);
            self.____finally = null;
        }
    };
 
    this.exec = function() //support for custom function 
    {
        var args = [].slice.call(arguments,1),func = arguments[0];
        args.push(self.____next);
        self.____items.push(function()
        {
            func.apply(obj,args);
        });
        return self;
    };
 
    this.end = function(func) //support for final function 
    {
        self.____finally = func;
        return self;
    };
 
    //copy and wrap the methods of obj 
    for(var func in obj)
    {
        if (typeof obj[func] == 'function' && obj.hasOwnProperty(func))
        {
            (function(func)
            {
                self[func] = function()
                {
                    var args = [].slice.call(arguments);
                    args.push(self.____next); //pass next callback to the last argument 
                    self.____items.push(function() //wrap the function and push into callbacks array 
                    {
                        obj[func].apply(obj,args);
                    });
                    return self; //always return JSChain it self like jQuery 
                }
            })(func); // this is the closure tricks 
        }
    }
 
    //start execute the chained functions in next tick 
    setTimeout(self.____next,0);
    return this;
}

##Advanced features##

###end method###

An end method can add a function to the end of the chain. You can not define this in the object when new JSChian().

###jump to the end instead of going to next###

When you call next method, if you pass a true value into next() method, that means JUMP TO THE END.

###data passing along functions###

var obj = 
{
    a: function(i,next)
    {
        this.A = i.toUpperCase();
        next();
    },
    b: function(next)
    {
        this.B = this.A+'B';
        next();
    }
};
var c = new JSChain(obj);
c.a('a')
.b()
.exec(function()
{
    console.log(this);
});

this will output:

{ a: [Function], b: [Function], A: 'A', B: 'AB' }