Question

I have two questions regarding the following function. Obviously, it is about a chat. In the function chat() different functions are called, one to establish a connection, one to search for someone to chat with (randomly), and one to get messages every second.

function chat()
{
    //Open connection
    var openconnection=openConnection();
    //Stop function if connection could not be established
    if(openconnection==false) return;

    //Search for someone to chat with
    searchforcontact=searchForContact();
    if(searchforcontact==false) return;

    //Constantly get messages
    setTimeout(function(){
        setInterval(getMessages(),1000);
    },2000);
}

function openConnection() { 
    //Establish connection to php script 
    $.ajax({ 
        type: 'POST', 
        url: 'action/chat/openconnection.php', 
        success: function(connection) { 
            //Let user know that someone to chat with is searched for 
            $('#chatTextDiv').append('bla'); 
            //Return that the connection was successfull 
            return true; 
        } 
    }).error(function() { 
        //Let user know that a connection could not be established 
        $('#chatTextDiv').append('bla'); 
        //Return false 
        return false; 
    }); 
}

Here are my questions:

1: I use return to stop the function chat() if, e.g., a connection could not be established. However the functions goes on to searchForContact(), and even if that fails, still goes on. How come?

2: The function getMessages() only runs once, I wonder why? FYI, I use the timeout for usability.

Answer 1

Most likely openConnection() doesn’t return false. Since synchronous API are very uncommon and not really useable from within JavaScript, I am pretty sure, that openConnection does not work the way you use it. Please provide more information on the openConnection function.

Also, instead of passing the getMessages function to the call to setInterval, you invoke getMessages and pass whatever it returns to setInterval. This is most likely not what you want. You should change that call to the following:

setTimeout(function(){
    setInterval(getMessages,1000);
},2000);

You should really read up on how AJAX and asynchronous APIs in general work. To give you a head-start here is an update to your code that should demonstrate what you’re doing wrong:

function openConnection(success, error) { 
    //Establish connection to php script 
    $.ajax({ 
        type: 'POST', 
        url: 'action/chat/openconnection.php', 
        success: success
    }).error(error||function () {}); 
}

function chat(ready) {
    //Open connection
    openConnection(function () {
        // If this function is called, then the connection is established

        //Search for someone to chat with
        searchforcontact=searchForContact();
        if(searchforcontact==false) return;

        // I STRONGLY SUPPOSE searchForContact is also an asynchronous API!

        //Constantly get messages
        setTimeout(function(){
            setInterval(getMessages,1000);
            ready();
        },2000);
    }, function () {
        // when this function is called, something went wrong.
    });
}

chat(function () {
    // when this function is called, chat is ready to be used!
});