function longRunningOperation(callback) { 
    // simulate a 3 second operation 
    setTimeout(callback, 3000); /*from xlrtb.cn*/
} 

function userClicked() { 
    console.log("starting a long operation"); 
    longRunningOperation(function () {
         console.log("ending a long operation");
    }); 
} 
// simulate a user action 
userClicked();