jschain

Chain style sequentially programming for Javascript asynchronous jobs.

npm install jschain
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Javascript Chain

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

Install

npm install jschain

Quick Start

new JSChain(
{
    foo: function(next)
    {
        console.log('foo');
        setTimeout(next,1000);
    },
    bar: function(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);
}).exec(function()
{
    console.log('done');
});

Background

Old days, you might write something 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(
{
    foo: function(next)
    {
        console.log('foo');
        setTimeout(next,1000);
    },
    bar: function(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);
}).exec(function()
{
    console.log('done');
});

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

var myController = 
{
    ajaxGet: function(next) {  ... ... next(); ... },
    saveToDatabase: function(a,next){ ... ... next(); },
    notifyUser: function() {  ... arguments[arguments.length-1].call(); ... },
    markNotified: function(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 tiny. 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.____next = function()  //execute next function
    {
        var func = self.____items.shift();
        if (func) func.call();
    };

    this.exec = function() //support for custom function
    {
        var args = [].slice.call(arguments,1);
        args.push(self.____next);
        var func = arguments[0];
        self.____items.push(function()
        {
            func.apply(obj,args);
        });
        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); //change arguments as an array
                    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 trick
        }
    }

    //start execute the chained functions in next tick
    setTimeout(function()
    {
        self.____next();
    },0);

    return this;
}

Good luck.

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