Question

I’m trying to create my own class for logging errors and messages to a database, but I’m new to creating custom classes and methods in Javascript. After plenty of research, I was able to put together the following code:

    function log ()
    {
    }

    log.error = function (currentFunction, logMessage)
    {
        createLog (currentFunction, logMessage, "Error");
    }

And I’m able to call the log.error function successfully with:

    log.error("current function name", "this is my error message");

My question is this: Most of the sites I looked at said to organize your code like this instead:

    function log ()
    {
        this.error = function (currentFunction, logMessage)
        {
            createLog (currentFunction, logMessage, "Error");
        }
    }

But whenever I try to call that error function, I get the following error:

Cannot find function error in object function log(currentFunction, logMessage)

Does anyone know why this is? For the sake of keeping my code clean, I would really like to be able to place everything inside one function, but at this point it looks like I may have to separate everything out, as in the first code block above.

EDIT – MY SOLUTION

Thanks to both dystroy and Jose Vega (sorry Jose, I don’t have enough reputation to up-vote your answer). I ended up using dystroy’s solution simply because I feel it will be easier for me to maintain my code in the future, however Jose’s answer helped give me insight into what I was trying to do and the different options available to me. I feel I have a much better grasp on what’s going on when you do something like var objectName = {} vs function className () {}.

Here’s my new code:

    function log ()
    {
        log.prototype.error = function (currentFunction, logMessage)
        {
            createLog (currentFunction, logMessage, "Error");
        }

        log.prototype.warning = function (currentFunction, logMessage)
        {
            createLog (currentFunction, logMessage, "Warning");
        }

        log.prototype.info = function (currentFunction, logMessage)
        {
            createLog (currentFunction, logMessage, "Info");
        }

        function createLog (currentFunction, logMessage, messageType)
        {
            //code that updates MSSQL database
        }
    }

Answer 1

You’re not using classes at all and your first function called log is totally useless as you call it.

You could have written it as

var log = {}

log.error = function (currentFunction, logMessage){
    createLog (currentFunction, logMessage, "Error");
}

Usually, when you create a new function and want to see it as a class, you do like this :

function log () {
}
log.prototype.error = function (currentFunction, logMessage) {
    createLog (currentFunction, logMessage, "Error");
}

And then you may use it like this :

(new log()).error("current function name", "this is my error message");

This looks a little like your second example, except that the error function is shared by all instances of log it you attach it to the prototype.

The MDN has a document about the object model in javascript.