#chain-of-custody Chain of Custody design pattern for cleanly dealing with sequences of operations that may be asynchronous. ##Install npm install chain-of-custody

##Usage There are two key components, ChainItem and ChainBuilder. You won't care about ChainItem. The intent is to create a nice, readable chain of steps that are executed one by one with a generate way to exit the chain (i.e. by using an event) in the event of a failure.

###Example

import {ChainBuilder} from './../lib';
import {ICaughtException} from './../lib';
import * as fs from 'fs';

let chainBuilder = new ChainBuilder((data, next, error) => {
    fs.readFile(`${__dirname}/test.json`, 'UTF-8', (err, data) => {
        if(err){
            error(err);
        } else {
            next(data);
        }
    });
}).then((data, next, error) => {
    let json = JSON.parse(data.toString());
    json.updated = true;
    next(json);
}).then((data, next, error) => {
    fs.writeFile(`${__dirname}/tested.json`, JSON.stringify(data), (err) => {
        if(err){
            error(err);
        } else {
            next();
        }
    });
});

chainBuilder.on('exception', (err : ICaughtException) => {
    console.log(err);
});

chainBuilder.on('error', (err)=>{
    console.log(err);
});

chainBuilder.on('done', () => {
    console.log('ok');
});

chainBuilder.execute();

##API ###ChainBuilder::constructor(closure : (data?:any, next:(data?:any)=>void, error:(data?:any)=>void)) ###ChainBuilder::execute(data?:any):void Takes any data object as an initializer, if desired. ###ChainBuilder::then(closure : (data?:any, next:(data?:any)=>void, error:(data?:any)=>void)):void Next step in the chain. Must be a closure of that type. ###Events There are three events.

• 'done' indicates that the chain has completed execution.
• 'error' indicates that the chain has exited early due to an error condition because logic in the chain explicitly called the error function.
• 'exception' indicates that there was an uncaught exception in the chain that was caught in ChainBuilder. The error object produced is an ICaughtException that contains an exception attribute (the exception object), and the data so that the state of the chain can be evaluated.

##Executing from Source The project is written in TypeScript because TypeScript is amazing. To get this to work, npm install -g typescript and then to get the typings support npm install -g typings and then run npm install in the project directory.