var ctx = SP.ClientContext.get_current();

var factory = new SP.ProxyWebRequestExecutorFactory(this.appWebUrl);
ctx.set_webRequestExecutorFactory(factory);

var appContextSite = new SP.AppContextSite(ctx, caller.parent.srcUrl);
var hostweb = appContextSite.get_web();
ctx.load(hostweb);
console.log("URL: "+hostweb.get_lists().get_count());