How can I make this javascript easier to read, maintain, and understand from an OO background?

Question

I come from the land of Java, C#, etc. I am working on a javascript report engine for a web application I have. I am using jQuery, AJAX, etc. I am having difficulty making things work the way I feel they should - for instance, I have gone to what seems like too much trouble to make sure that when I make an AJAX call, my callback has access to the object's members. Those callback functions don't need to be that complicated, do they? I know I must be doing something wrong. Please point out what I could be doing better - let me know if the provided snippet is too much/too little/too terrible to look at.

What I'm trying to do:

• On page load, I have a select full of users.
• I create the reports (1 for now) and add them to a select box.
• When both a user and report are selected, I run the report.
• The report involves making a series of calls - getting practice serieses, leagues, and tournaments - for each league and tournament, it gets all of those serieses, and then for each series it grabs all games.
• It maintains a counter of the calls that are active, and when they have all completed the report is run and displayed to the user.

Code:

//Initializes the handlers and reports
function loadUI() {
    loadReports();
    $("#userSelect").change(updateRunButton);
    $("#runReport").click(runReport);
    updateRunButton();
    return;
    $("#userSelect").change(loadUserGames);
    var user = $("#userSelect").val();
    if(user) {
        getUserGames(user);
    }
}

//Creates reports and adds them to the select
function loadReports() {
    var reportSelect = $("#reportSelect");
    var report = new SpareReport();
    engine.reports[report.name] = report;
    reportSelect.append($("<option/>").text(report.name));

    reportSelect.change(updateRunButton);
}

//The class that represents the 1 report we can run right now.
function SpareReport() {
    this.name = "Spare Percentages";
    this.activate = function() {

    };

    this.canRun = function() {
        return true;
    };

    //Collects the data for the report.  Initializes/resets the class variables,
    //and initiates calls to retrieve all user practices, leagues, and tournaments.
    this.run = function() {
        var rC = $("#rC");
        var user = engine.currentUser();
        rC.html("<img src='/img/loading.gif' alt='Loading...'/> <span id='reportProgress'>Loading games...</span>");
        this.pendingOperations = 3;
        this.games = [];
        $("#runReport").enabled = false;
        $.ajaxSetup({"error":(function(report) {
            return function(event, XMLHttpRequest, ajaxOptions, thrownError) {
                report.ajaxError(event, XMLHttpRequest, ajaxOptions, thrownError);
            };
        })(this)});

        $.getJSON("/api/leagues", {"user":user}, (function(report) {
            return function(leagues) {
                report.addSeriesGroup(leagues);
            };
        })(this));
        $.getJSON("/api/tournaments", {"user":user}, (function(report) {
            return function(tournaments) {
                report.addSeriesGroup(tournaments);
            };
        })(this));
        $.getJSON("/api/practices", {"user":user}, (function(report) {
            return function(practices) {
                report.addSerieses(practices);
            };
        })(this));
    };

    // Retrieves the serieses (group of IDs) for a series group, such as a league or
    // tournament.
    this.addSeriesGroup = function(seriesGroups) {
        var report = this;
        if(seriesGroups) {
            $.each(seriesGroups, function(index, seriesGroup) {
                report.pendingOperations += 1;
                $.getJSON("/api/seriesgroup", {"group":seriesGroup.key}, (function(report) {
                    return function(serieses) {
                        report.addSerieses(serieses);
                    };
                })(report));
            });
        }
        this.pendingOperations -= 1;
        this.tryFinishReport();
    };

    // Retrieves the actual serieses for a series group.  Takes a set of
    // series IDs and retrieves each series.
    this.addSerieses = function(serieses) {
        var report = this;
        if(serieses) {
            $.each(serieses, function(index, series) {
                report.pendingOperations += 1;
                $.getJSON("/api/series", {"series":series.key}, (function(report) {
                    return function(series) {
                        report.addSeries(series);
                    };
                })(report));
            });
        }
        this.pendingOperations -= 1;
        this.tryFinishReport();
    };

    // Adds the games for the series to the list of games
    this.addSeries = function(series) {
        var report = this;
        if(series && series.games) {
            $.each(series.games, function(index, game) {
                report.games.push(game);
            });
        }
        this.pendingOperations -= 1;
        this.tryFinishReport();
    };

    // Checks to see if all pending requests have completed - if so, runs the
    // report.
    this.tryFinishReport = function() {
        if(this.pendingOperations > 0) {
            return;
        }
        var progress = $("#reportProgress");
        progress.text("Performing calculations...");
        setTimeout((function(report) {
            return function() {
                report.finishReport();
            };
        })(this), 1);
    }

    // Performs report calculations and displays them to the user.
    this.finishReport = function() {
        var rC = $("#rC");

        //snip a page of calculations/table generation
        rC.html(html);

        $("#rC table").addClass("tablesorter").attr("cellspacing", "1").tablesorter({"sortList":[[3,1]]});
    };

    // Handles errors (by ignoring them)
    this.ajaxError = function(event, XMLHttpRequest, ajaxOptions, thrownError) {
        this.pendingOperations -= 1;
    };

    return true;
}

// A class to track the state of the various controls.  The "series set" stuff
// is for future functionality.
function ReportingEngine() {
    this.seriesSet = [];
    this.reports = {};
    this.getSeriesSet = function() {
        return this.seriesSet;
    };
    this.clearSeriesSet = function() {
        this.seriesSet = [];
    };
    this.addGame = function(series) {
        this.seriesSet.push(series);
    };
    this.currentUser = function() {
        return $("#userSelect").val();
    };
    this.currentReport = function() {
        reportName = $("#reportSelect").val();
        if(reportName) {
            return this.reports[reportName];
        }
        return null;
    };
}

// Sets the enablement of the run button based on the selections to the inputs
function updateRunButton() {
    var report = engine.currentReport();
    var user = engine.currentUser();
    setRunButtonEnablement(report != null && user != null);
}

function setRunButtonEnablement(enabled) {
    if(enabled) {
        $("#runReport").removeAttr("disabled");
    } else {
        $("#runReport").attr("disabled", "disabled");
    }

}

var engine = new ReportingEngine();

$(document).ready( function() {
    loadUI();
});

function runReport() {
    var report = engine.currentReport();
    if(report == null) {
        updateRunButton();
        return;
    }
    report.run();
}

I am about to start adding new reports, some of which will operate on only a subset of user's games. I am going to be trying to use subclasses (prototype?), but if I can't figure out how to simplify some of this... I don't know how to finish that sentence. Help!

Answer 1

$.getJSON("/api/leagues", {"user":user}, (function(report) {
        return function(leagues) {
            report.addSeriesGroup(leagues);
        };
    })(this));

Can be written as:

var self = this;
$.getJSON("/api/leagues", {"user":user}, (function(leagues) {
            self.addSeriesGroup(leagues);
        });

The function-returning-function is more useful when you're inside a loop and want to bind to a variable that changes each time around the loop.

Answer 2

Provide "some" comments where necessary.

Answer 3

I'm going to be honest with you and say that I didn't read the whole thing. However, I think there is something about JavaScript you should know and that is that it has closures.

var x = 1;
$.ajax({
  success: function () {
    alert(x);
  }
});

No matter how long time it takes for the AJAX request to complete, it will have access to x and will alert "1" once it succeeds.

Answer 4

Understand Closures. This takes some getting used to. (which, many will use, and is certainly the typical way of going about things, so it's good if you understand how that's happening)

This is a good thread to read to get a simple explanation of how to use them effectively.

Answer 5

You should use prototypes to define methods and do inheritance:

function Parent(x) {
  this.x = x;  /* Set an instance variable. Methods come later. */
}

/* Make Parent inherit from Object by assigning an
 * instance of Object to Parent.prototype. This is
 * very different from how you do inheritance in
 * Java or C# !
 */
Parent.prototype = {  /* Define a method in the parent class. */
  foo: function () {
    return 'parent ' + this.x;  /* Use an instance variable. */
  }
}

function Child(x) {
  Parent.call(this, x)  /* Call the parent implementation. */
}

/* Similar to how Parent inherits from Object; you
 * assign an instance of the parent class (Parent) to
 * the prototype attribute of the child constructor
 * (Child).
 */
Child.prototype = new Parent();

/* Specialize the parent implementation. */
Child.prototype.foo = function() {
  return Parent.prototype.foo.call(this) + ' child ' + this.x;
}

/* Define a method in Child that does not override
 * something in Parent.
 */
Child.prototype.bar = function() {
  return 'bar';
}

var p = new Parent(1);
alert(p.foo());

var ch = new Child(2);
alert(ch.foo());
alert(ch.bar());

I'm not familiar with jQuery, but I know the Prototype library (worst name choice ever) has some functionality that make it easier to work with inheritance.

Also, while coming up with the answer to this question, I found a nice page that goes into more detail on how to do OO right in JS, which you may want to look at.