The Durandal core is made up of 8 modules. The system.js module provides core functionality to Durandal and it is also useful for any custom modules we write in our own apps.

Features

• Logging
• Debug mode
• Object Type Testing
• noop function
• console.log polyfill
• Object.keys polyfill
• gets and sets the __moduleId__ of an object
• Creates seam to use your preferred promise implementation

Architecture

• AMD Module
• system is an object literal. There is only one instance.
• Lines: 427
• Documentation is done with YUIDoc – Javascript Documentation Tool

Dependencies

• requireJs
• jQuery
• No other durandal dependencies
• Every module in durandal depends on system

Debug mode

system.debug(true); 

• turns debug mode on
• logs to the console and throw errors

Debug is off by default

system.debug(false);

• turns debug mode off
• no logging and no error throwing
• uses the noop function until turned on

Interesting uses of JavaScript

Reflection

Object.keys(obj);

Returns an array of strings representing all the enumerable property names of the object

Make shortcuts to native JavaScript functions

 var nativeKeys = Object.keys,
     hasOwnProperty = Object.prototype.hasOwnProperty,
     toString = Object.prototype.toString,
     nativeIsArray = Array.isArray,
     slice = Array.prototype.slice;

The noop function (No Operation)

 var noop = function() { };

 Define a function that does nothing and set it as a default 
 to be replaced later during configuration if desired.

Arguments and parameters

You can refer to a functions parameters by name or by using the arguments array

Test the number of arguments and take different actions.

if (arguments.length == 1) {};

Refer to arguments by index

var first = arguments[0];       

Accept n number of arguments in a function.

function(obj) {         

    //do something with obj

    var rest = slice.call(arguments, 1);    
    for (var i = 0; i < rest.length; i++) {
        var source = rest[i];

        if (source) {
            //do something with the rest of the arguments
        }
    }
}

Public Api

Official system.js documentation is here >>

My summary of the api

version - durandal version
noop - no operation function
getModuleId - gets \_\_moduleId\_\_
setModuleId - sets \_\_moduleId\_\_
resolveObject - returns either the object or news it up from a function
debug - turns debug mode on and off
log - logs to console. noop by default
error - noop by default
assert - throws and error only in debug mode
defer - wraps the jquery defer.  Lets you replace it with a different implementation
guid - simple guid
acquire - returns modules from requireJs
extend - copies properties from n number of functions onto an object and returns the extended object
wait - waits specified number of seconds and returns a promise
keys- polyfills the getKeys behavior

is Functions to test object types

isElement
isArray
isObject
isBoolean
isPromise
isArguments
isFunction
isString
isNumber
isDate
isRegExp