Chaining Tatum

A utility library that assists in method chaining of async functions. Mixing async with sync method especially when they are being called serially results in a very verbose code. There are unecessary callbacks and overuse of the then method.

Example

var baseUrl = 'http://www.product.com/'

//Returns a value
var sum = function (a, b){
    return a + b;
}


//Returns a promise, that resolves into the product of two numbers
var product = function (a, b){
    return http.get(baseUrl + a + '/' +b);
}

There are two functions sum and product. The sum instantly adds the two arguments and returns a value where as product makes an async http request to get the product of two numbers.

Usage without chaining-tatum

var startValue = 10,
    finalValue;

var a = sum(startValue, 20);

product(a, 100)
    .then(function (productWith100){
        return sum(50, productWith100);
    })
    .then(function (sumWith50){
        return product(1000, sumWith50);
    })
    .then(function(productWith1000){
        finalValue = productWith1000;
    });

Usage with chaining-tatum

var Chain = require('chaining-tatum').Chain;

//Create a prototype object
var proto = {
    sum: sum,
    product: product
}

var chained = new Chain(proto);

chained
    .sum(20) //sum(10, 20) := 30
    .product(100) //product(100, 30) := 130 as a promise
    .sum(50)
    .product(1000)
    .$launch(startValue)
    .then(function(value){
        finalValue = value;
    });

The execution doesn't happen until the $launch method is called with some initial value. The initial value is set into the memory and is used as the second parameter to the sum method, first being the value 20. The value is calculated by calling the sum method and then is passed as the second argument to the product method, first being 100 in this case.

product method returns a promise, only when that is resolved it is passed to the next sum method call with 50 as the second param and 130 as the first param.

This makes the code much more readable and one doesn't need to know if the function returns a promise or not.

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