"method overloading" in javascript

Question

So I admit that I'm new to javascript and that I come from a C.+ background ("Hi, I'm Bob, I'm a class-based static language user", chorus "hi Bob!").

I find that I often end up writing functions like:

function someFunc()
{
    if (arguments.length === 0 ){
       ...
    } else {
       ...
    }
}

(where there might be three such cases). Or, alternatively, I write the difference into the name:

function someFuncDefault() { ... };
function someFuncRealArg(theArg) { ... };

(Substitute "RealArg" for some semantically contentful phrase).

Is there a better pattern for this kind of thing?

Answer 1

I don't know that I would do it this way, but it seems like it might make your code mildly less unmanageable:

function someFunc() {
    switch (arguments.length) {
        case 0: noArgs();
        case 1: oneArg(arguments[0]);
        case 2: twoArgs(arguments[0], arguments[1]);
    }
    function noArgs() {
        // ...
    }
    function oneArg(a) {
        // ...
    }
    function twoArgs(a, b) {
        // ...
    }
}

Another example might be:

function someFunc(a, b) {
    if ('string' == typeof a) {
        // ...
    } else if ('number' == typeof a) {
        // ...
    }
}

And of course you can probably create something quite unmanageable by combining both examples (using conditions to determine behaviour based on number of arguments and types of arguments).

Answer 2

This is overloading, not overriding no?

Javascript is weakly typed, so method signatures and native support is out. My recommendation is to pass an extensible object as the solitary argument. Inspect and handle the existance of properties on the param object as you wish.

What advantage does this have over arguments? Well it lets you be explicit about your intentions where you call, and unambiguous about the meaning of arg1 and arg2 where you recieve, and it lets you abstract to a custom data object class you can extend functionality to.

function someFunc(params)
{
  var x = params.x || defaultX;
  var y = params.y || defaultY;

  //businesslogic
}

someFunc({x:'foo',y:'bar'});

someFunc({y:'baz'});