Long Polling for jQuery

long-polling.jquery.js

/* Long Polling
 * 
 * By: Ivan Montiel
 */

jQuery.poll = function (options, poll) {
	if ( poll == null || poll === undefined) {
		poll = {};
	}
	
	if ( (typeof options) == "string") {
		options = {command : options};
	}
	
	var defaults = {
		prevDataLength : 0,
		nextLine : 0,
		http : null, 
		pollTimer : null,
	    command : "poll",
		url : "",
		data : "",
		update : null,
		stop : false
	};
		
	var createRequestObject = function () {
		if (window.XMLHttpRequest) {
            defaults.http = new XMLHttpRequest();
	    } else {
	    	defaults.http = new ActiveXObject("Microsoft.XMLHTTP");
	    }
		
	    if (!defaults.http)
            debug("Couldn't start XMLHttpRequest object");
	};
	var handleResponse = function () {
		if (defaults.http.readyState != 4 && defaults.http.readyState != 3)
            return;
        if (defaults.http.readyState == 3 && defaults.http.status != 200) {
            return;
            clearInterval(defaults.pollTimer);
            defaults.inProgress = false;
        }
        // In konqueror http.responseText is sometimes null here...
        if (defaults.http.responseText === null)
            return;

        while (defaults.prevDataLength != defaults.http.responseText.length && !defaults.stop) {
            if (defaults.http.readyState == 4  && defaults.prevDataLength == defaults.http.responseText.length)
                break;
            defaults.prevDataLength = defaults.http.responseText.length;
            var response = defaults.http.responseText.substring(defaults.nextLine);
            var lines = response.split('\n');
            defaults.nextLine = defaults.nextLine + response.lastIndexOf('\n') + 1;
            if (response[response.length-1] != '\n')
                lines.pop();

            for (var i = 0; i < lines.length; i++) {
                defaults.update(lines[i]);
            }
        }
        
        if ( defaults.stop) {
        	defaults.http.abort();
        	clearInterval(defaults.pollTimer);
        }

        if ((defaults.http.readyState == 4 && defaults.prevDataLength == defaults.http.responseText.length))
            clearInterval(defaults.pollTimer);

        defaults.inProgress = false;
    };
		
	var startProcess = function () {	
		createRequestObject();
		var appendData = "";
		if (defaults.data) {
			appendData = "?" + defaults.data;
		}
		defaults.http.open('get', defaults.url + appendData);
    
		defaults.http.onreadystatechange = handleResponse;
		defaults.http.send(null);

		defaults.pollTimer = setInterval(handleResponse, 1000);
    };
    
	var options = $.extend(defaults, options);
	
	if ( defaults.command == "poll") {
		startProcess();
	}
	else if (defaults.command == "stop") {
		poll.stop = true;
	}
	
	return defaults;
};