jsonp + lscache

jsonp.js

//Lightweight JSONP fetcher - www.nonobtrusive.com
var JSONP = (function(){
  var counter = 0, head, query, key, window = this;
  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 jsonp(url, params, callbackParam, callbackFunc) {
    query = "?";
    params = params || {};
    for ( key in params ) {
      if ( params.hasOwnProperty(key) ) {
        query += key + "=" + params[key] + "&";
      }
    }
    // Check if its in localStorage first, immediately callback if so
    var lskey = url + query;
    var data = lscache.get(lskey);
    if (data) {
      callbackFunc(data);
    } else {
      var jsonp = "json" + (++counter);
      window[ jsonp ] = function(data){
        callbackFunc(data);
        // Store there for 30 minutes 
        lscache.set(lskey, data, 60*30);
        window[ jsonp ] = null;
        try {
          delete window[ jsonp ];
        } catch (e) {}
      };
      var callbackParam = callbackParam || 'callback'; 
      load(url + query + callbackParam + "=" + jsonp);
    }
    return jsonp;
  }
  return {
    get:jsonp
  };
}());