Passing multiple optional parameters in JavaScript

Question

In Lua I've made my own Event system and I wanted to convert and use it in JavaScript, here's the code in Lua:

TriggerEvent = function(Name, ...)
    local EventID = nil;

    for Event2ID, Table in pairs(Event) do
        if(Table.Active and Table.Name == Name) then
            EventID = Event2ID;
            break;
        end
    end

    if(EventID == nil) then
        return false;
    end

    for ListenerID, Table in pairs(Event[EventID].Listener) do
        if(Table.Active) then
            Table.Function(...);
        end
    end
    return true;
end

Which works flawlessly. Here's what I have for JavaScript:

TriggerEvent = function(Name, ...) {
    var
        EventID = undefined
    ;

    for(Event2ID = 0, Length = Event.length; Event2ID < Length; Event2ID++) {
        if(Event[Event2ID].Active && Event[Event2ID].Name == Name) {
            EventID = Event2ID;
            break;
        }
    }

    if(EventID == undefined) {
        return false;
    }

    for(ListenerID = 0, Length = Event[EventID].Listener.length; ListenerID < Length; ListenerID++) {
        if(Event[EventID].Listener[ListenerID].Active) {
            Event[EventID].Listener[ListenerID].Function(...);
        }
    }
    return true;
}

Which doesn't work at all.

Example usage:

WebsiteConnected = function(Website, Test) {
    Website.SetTitle("Hello World");

    console.log(Website.GetTitle() + " connected! " + Test);
    return true;
}

CreateEvent("WebsiteConnected"); // Moved down.
AddEventListener("WebsiteConnected", WebsiteConnected);
TriggerEvent("WebsiteConnected", (Website || {}), "Test"); // Moved down.

I just tried it based on what I read from that article, but it did not work too well for me. Mind giving an example showing how to do what I'm trying to do? — SkittlesAreFalling
– SkittlesAreFalling, Commented Aug 19, 2014 at 14:18

Vivian River · Accepted Answer · 2014-08-19 14:18:12Z

3

Here's how "optional" arguments work in Javascript:

If you write a function like so:

function doSomething(arg1, arg2, arg3) {
    // Insert quality code here :-)
}

It is valid Javascript to call this function (or any other function for that matter) with any number of arguments.

If you pass in less than the three arguments specified, the remaining arguments will default to null.

If you pass in more than three arguments, the extra arguments will be ignored.

If you want to "overload" a function, there is no such thing in Javascript. If a function needs to accept two different types for one parameter, the function must check the type of what is passed in and behave accordingly.

Also, there is the arguments object, which provides an array-like interface to the arguments passed to the currently executing function. For some reason, there was a quirk in the development of the language that the arguments object behaves much like an array, but isn't an array. :-/

answered Aug 19, 2014 at 14:18

Vivian River

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6 Comments

SkittlesAreFalling Over a year ago

In other words, what I'm trying to do isn't possible?

hindmost Over a year ago

the remaining arguments will default to null. AFAIK they will default to undefined

SkittlesAreFalling Over a year ago

Okay thank you, I'll just pass an object with the variables I want inside.

Vivian River Over a year ago

For what it's worth, that's how a lot of functions in the popular jQuery library work. They take one argument that contains a number of fields.

jlewkovich Over a year ago

In this example, is there a way to pass in arg1 and arg3 but not arg2?

|

SkittlesAreFalling · Accepted Answer · 2014-12-31 21:23:20Z

I made a work around for what I was previously requesting, here's my system:

// ------------------------------------------------------------------------------------------------- Event "Class"
Event = function() {
    var
        Public = this,
        Private = {}
    ;

    Public.Create = function(Name) {
        if(Private.Created) {
            return false;
        }

        Private.Created = true;
        Private.Name = Name;
        Private.Function = [];
        return true;
    }

    Public.Delete = function() {
        if(! Private.Created) {
            return false;
        }

        Private = {};
        Private.Created = false;
        return true;
    }

    Public.IsCreated = function() {
        if(! Private.Created) {
            return false;
        }
        return true;
    }

    Public.SetName = function(Name) {
        if(! Private.Created) {
            return false;
        }

        Private.Name = Name;
        return true;
    }

    Public.GetName = function() {
        var
            Name = ""
        ;

        if(! Private.Created) {
            return Name;
        }

        Name = Private.Name;
        return Name;
    }

    Public.AddFunction = function(Function) {
        if(! Private.Created) {
            return false;
        }

        for(var FunctionID = 0, Length = Private.Function.length; FunctionID < Length; FunctionID++) {
            if(Private.Function[FunctionID] == Function) {
                return false;
            }
        }

        Private.Function[Private.Function.length] = Function;
        return true;
    }

    Public.HasFunction = function(Function) {
        if(! Private.Created) {
            return false;
        }

        for(var FunctionID = 0, Length = Private.Function.length; FunctionID < Length; FunctionID++) {
            if(Private.Function[FunctionID] == Function) {
                return true;
            }
        }
        return false;
    }

    Public.Call = function() {
        if(! Private.Created) {
            return false;
        }

        var 
            Arguments = ""
        ;

        for(var argumentID = 0, Length = arguments.length; argumentID < Length; argumentID++) {
            Arguments += "arguments[" + argumentID + "]";

            if(argumentID != (arguments.length - 1)) {
                Arguments += ", ";
            }
        }

        for(var FunctionID = 0, Length = Private.Function.length; FunctionID < Length; FunctionID++) {
            eval("Private.Function[FunctionID](" + Arguments + ")");
        }
        return false;
    }

    Public.Create(arguments[0]);
    return Public;
}

var
    TestEvent = new Event("TestEvent")
;

TestEvent.AddFunction(
    function() {
        console.log("TestEvent called.");
    }
);

TestEvent.AddFunction(
    function(String, String1) {
        console.log(String1 + String);
    }
);

TestEvent.Call("world!", "Hello ");

This works flawlessly. I've ran many benchmark tests.

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