Question

I have searched and read for a few hours yet I still cant understand the basic design pattern for creating a new object that has a choice of different methods (of the same name) that is set dependant on one of the arguments. here’s some code to explain what I am trying to do.
All advice and alternative approaches welcome. I hope someone can emancipate me form this cloud of ignorance.
Thanks

function BaseConstructor(whichMethods) {
    if (whichMethods==='a') {
         // do something to incorporate methodSetA
    }
    else if (whichMethods==='b') {
        // do something to incorporate methodSetB
    }

    this.init();
};

var methodSetA = {
    init: function() {
        // do initialisation A way
    },
    speak: function() {
        alert('i speak AAA way')
    }
};

var methodSetB = {
    init: function() {
        // do initialisation B way
    },
    speak: function(){
        alert('i got BBB all the way')
    }
};

thing = new BaseConstructor('b'); 
// b is an instance of BaseConstructor and has done the bWay init() function

thing.speak() // return alert 'i got BBB all the way'

Answer 1

You can do it like this using a factory function (a regular function that creates the appropriate object for you):

function BaseConstructor(whichMethods) {
    var elem;
    if (whichMethods==='a') {
         elem = new MethodSetA();
    } else if (whichMethods==='b') {
         elem = new MethodSetB();
    } else {
         // figure out what to do here if whichMethods is neither of the previous options
    }

    elem.init();
    return(elem);
};

And invoke it as a regular function call:

var thing = BaseConstructor('b');
thing.speak();

Note: there is no use of new with BaseConstructor() as it’s a regular function call.