Basic JSON XMLHttpRequest implementation.

json-http.js

var jsonHttp = function jsonHttp( ){
	var xmlHttpEngine = {
		"xmlHttp": new XMLHttpRequest( )
	};
	
	var requestSet = { 
		"querySet": { },
		"parameterSet": { },
		"headerSet": {
			"Content-Type": "application/json;charset=UTF-8"
		},
		"URL": "/",
		"method": "HEAD"
	};
	
	var include = function include( ){
		
	};
	
	var define = function define( ){
		
	};
	
	var setURL = function setURL( URL ){
		requestSet.URL = URL;
		
		return requestEngine;
	};
	
	var setMethod = function setMethod( method ){
		requestSet.method = method;
		
		return requestEngine;
	};
	
	var setHeader = function setHeader( headerSet ){
		for( var header in headerSet ){
			requestSet.headerSet[ header ] = headerSet[ header ];		
		}		
		
		requestSet.headerSet = Object.freeze( requestSet.headerSet );
		
		return requestEngine;
	};
	
	var setQuery = function setQuery( querySet ){
		for( var query in querySet ){
			requestSet.querySet[ query ] = querySet[ query ];		
		}	
		
		requestSet.querySet = Object.freeze( requestSet.querySet );
		
		return requestEngine;
	};
	
	var setParameter = function setParameter( parameterSet ){
		for( var parameter in parameterSet ){
			requestSet.parameterSet[ parameter ] = parameterSet[ parameter ];		
		}
		
		requestSet.parameterSet = Object.freeze( requestSet.parameterSet );
		
		return requestEngine;
	};
	
	var appendQuery = function appendQuery( URL ){
		var querySet = requestSet.querySet;
		
		var queryString = "";
		
		for( var query in requestSet.querySet ){
			queryString += [ query, querySet[ query ] ].join( "=" );
		}
		
		if( /\?/.test( URL ) &&
			/\&/.test( URL ) )
		{
			URL = [ URL, queryString ].join( "&" );				
			
		}else if( /\?/.test( URL ) ){
			URL = [ URL, queryString ].join( "" );
			
		}else{
			URL = [ URL, queryString ].join( "?" );
		}
		
		return URL;
	};
	
	var addHeader = function addHeader( xmlHttp, headerSet ){
		var xmlHttp = xmlHttpEngine.xmlHttp;
		
		for( var header in headerSet ){
			xmlHttp.setRequestHeader( header, headerSet[ header ] );
		}
	};

	var get = function get( URL ){
		requestEngine.setURL( URL );
		
		requestEngine.setMethod( "GET" );
		
		return requestEngine;
	};

	var post = function post( URL ){
		requestEngine.setURL( URL );
		
		requestEngine.setMethod( "POST" );
		
		return requestEngine;
	};
	
	var send = function send( onResponseCallback ){
		var xmlHttp = xmlHttpEngine.xmlHttp;
		
		xmlHttp.onreadystatechange = function onReadyStateChange( ){
			if( xmlHttp.readyState == 4 &&
				xmlHttp.status == 200 )
			{
				var result = JSON.parse( xmlHttp.responseText );
				
				onResponseCallback( null, result, xmlHttp );
				
			}else if( xmlHttp.readyState == 4 ){
				onResponseCallback( new Error( "request failed" ), null, xmlHttp );
			}
		};
		
		var URL = appendQuery( requestSet.URL );
		
		xmlHttp.open( requestSet.method, URL, true );
		
		addHeader( xmlHttp, requestSet.headerSet );
		
		try{
			xmlHttp.send( JSON.stringify( requestSet.parameterSet ) );
			
		}catch( error ){
			onResponseCallback( error, null, xmlHttp );
		}
		
		return requestEngine;
	};
	
	var requestEngine = { };
	
	Object.defineProperty( requestEngine, "get",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": get
		} );
		
	Object.defineProperty( requestEngine, "post",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": post
		} );
		
	Object.defineProperty( requestEngine, "send",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": send
		} );
		
	Object.defineProperty( requestEngine, "setHeader",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": setHeader
		} );
		
	Object.defineProperty( requestEngine, "setParameter",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": setParameter
		} );
		
	Object.defineProperty( requestEngine, "setQuery",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": setQuery
		} );
		
	Object.defineProperty( requestEngine, "setMethod",
		{
			"writable": false,
			"enumerable": false,
			"configurable": false,
			"value": setMethod
		} );
		
	return requestEngine;
};