JSONP Library

/*
* Lightweight JSONP fetcher
* Copyright 2010-2012 Erik Karlsson. All rights reserved.
* BSD licensed
*/


/*
* Usage:
*
* JSONP.get( 'someUrl.php', {param1:'123', param2:'456'}, function(data){
*   //do something with data, which is the JSON object you should retrieve from someUrl.php
* });
*/
var JSONP = (function(){
    var counter = 0, head, query, key, window = this, config = {};
    function load(url) {
        var script = document.createElement('script'),
            done = false;
        script.src = url;
        script.async = true;

        script.onload = script.onreadystatechange = function() {
            if ( !done && (!this.readyState || this.readyState === "loaded" || this.readyState === "complete") ) {
                done = true;
                script.onload = script.onreadystatechange = null;
                if ( script && script.parentNode ) {
                    script.parentNode.removeChild( script );
                }
            }
        };
        if ( !head ) {
            head = document.getElementsByTagName('head')[0];
        }
        head.appendChild( script );
    }
    function encode(str) {
        return encodeURIComponent(str);
    }
    function jsonp(url, params, callback, callbackName) {
        query = (url||'').indexOf('?') === -1 ? '?' : '&';
        params = params || {};
        for ( key in params ) {
            if ( params.hasOwnProperty(key) ) {
                query += encode(key) + "=" + encode(params[key]) + "&";
            }
        }
        var jsonp = "json" + (++counter);
        window[ jsonp ] = function(data){
            callback(data);
            try {
                delete window[ jsonp ];
            } catch (e) {}
            window[ jsonp ] = null;
        };

        load(url + query + (callbackName||config['callbackName']||'callback') + '=' + jsonp);
        return jsonp;
    }
    function setDefaults(obj){
        config = obj;
    }
    return {
        get:jsonp,
        init:setDefaults
    };
}());